Precisely.
And note the timeline: three months. Much shorter than readers of a book have to wait for the sequel.
Another thing to note is that MOVIES do not end in cliffhangers; TV shows do.
Back to the Future 2&3; released eight months apart. The first ended with "To be continued" as a hope it would create a clamor and enable funding for more. The second was tagged with "to be concluded" as a deliberate cliffhanger. Many theaters ran the short teaser trailer of the third immediately after--as the producers intended in order to build up interest.
The Matrix 2&3 were released a year apart. Again, like BTTF, they were filmed concurrently and designed to fill out a trilogy originating from a once stand-alone first movie.
The Lord of the Rings trilogy were each released a year apart. They were all filmed together and deliberately edited to create separate cliffhangers apart from those in the books.
Patriot Games was the second "Jack Ryan" book made into a movie. It was the first time Harrison Ford played the character. At the end of the movie, there is a very deliberate cliffhanger regarding one of his children. If one had read other Tom Clancy novels, one knew the answer. The movie-only fans had to wait until the funding, filming and release of
Clear & Present Danger.
In such an example, the readers were immediately satisfied and the film goers had to wait. It is a risky proposition for movies to have cliffhangers, unless the entire project is funded to completion, notwithstanding
The Perils of Pauline. TPoP weren't traditional cliffhangers as they always showed the resolution--just in case no more were filmed.
TV shows plan for multiple season runs but often things are left hanging when the series is abruptly canceled. Unless there is a guarantee of a new season, most showrunners now don't want the writers to do cliffhangers because it makes the show harder to resell later.
There's a difference between the two forms, and movies are more like novels than TV shows are. TV shows are designed so that they could potentially run forever (hasn't As the World Turns been on for over 40 years?!). The story goes on and on and on and on--it's more like an infinitely expanding short-story collection than like a novel. So you can have cliffhangers at the end of episodes or seasons; everyone knows the show will go on, and the mystery will be solved within a couple of months at most, sometimes less (if the cliffhanger is during the season at the end of one episode, it'll be resolved the next week).
TV shows are NOT designed to run forever, not even soaps. Daytime dramas were initially designed to reflect people's everyday dramas. Everyone's life goes on through all the chaos. Nearly every soap still on-air in the USA today started with a core set of characters and expanded. While some storylines have cliffhangers, they are within the framework of the rest of their universe continuing on...because they show has been renewed. When I read a short story collection, they are rarely set in the same universe, not written by collaborative writers and I can go back and enjoy them again and again in any order I care to read. This is completely impossible with soaps.
Quite a few soaps have departed over the last decade. Their writers wrapped up most of those storylines while leaving a few things open for the fans, and again, to give the sense "this world still goes on". There is a season to soaps, but rarely have cliffhangers between them been written. Once there was a set of companion soaps who shared the same universe. A big cross-over was planned. One soap was abruptly cancelled. It left the other one scrambling for their own storylines.
Movies and novels are designed to have a complete story contained within them.
This statement is incorrect. While many movies are written to be standalone, one-off products, quite often the writer(s) has more to the characters/universe and will happily write a sequel. Others are written as the first of unrealized multiples. Still others start out as standalones and are expanded for financial gains (see BTTF and Matrix examples above). Lastly, many movies are written to see just part of a story concerning just a couple of characters or a location or an item while not explaining everything. The story is deliberately incomplete to concentrate on the focus of whatever the writer deems worthy. There is no guaranteed conclusion.
As for novels, I don't know of a writer yet who has just one book about their characters, story or world. They may write a single book about one character, but it is often part of a larger scope present in their other work. The actual story may carry out well over the single novel.
TV series (other than miniseries, which are basically extra-long movies) and short story collections are not; the reader of short stories or the watcher of a TV series do not expect to have a complete, all-threads-wrapped-up story, whereas movie-goers and novel-readers do.
I have yet to see a movie (tv, theater or otherwise) which is complete story with all threads up. Something is always left open. When I read a short story, I don't expect a complete encapsulation of that world. I hope for a taste of something interesting. And then I hope the good ones wrote more.
"That's it, all of it, right there on the page or screen" is completely unrealistic. I have been disappointed by writers trying to make such hay. The attempts fall flat because they are unrealistic, there is nothing to relate to which makes it uninteresting to follow more.
I expect police procedurals (Law & Order, CSI, etc) to have at least one case being opened, investigated, and concluded during one episode. They generally also have one case or character or situation which carries over between other episodes (sometimes back-to-back, other times something is mentioned in season 2 and finally addressed in season 6). The heavy episodes also carry a third case which is never resolved. This is the formula: 1 main case wrapped up, 1 b case which may affect and/or interact with main case but makes sure everyone has something to do, and occasionally reference the c case which an ongoing puzzler that reveals personal information about the cast and is non-continuous.
If they didn't wrap everything up in one episode, it wouldn't be rewatchable because you would need all the other episodes to refer to in order to understand the story. Whereas I know Briscoe will arrest, McCoy will prosecute and Danny Tanner will have the girls in bed by 8. I rarely expect--or get--that same sense of completion with movies or novels.
A TV show can get away with a cliffhanger, just like a story in the middle of a collection can. But even with those, you can't put a cliffhanger in the last episode of the TV show or the last story in the collection; it has to come before then, so that the story can go on. And you can put cliffhangers at the end of chapters in a novel, or in scenes preceding the last scene in a movie, BUT NOT at the end. They only work where the story is going to continue relatively soon, as in a TV series or short-story collection or at the end of a chapter in the middle of a novel. But a year or two, which is how long it takes to get another book out (minimum), is not "soon." Not soon enough for cliffhangers at the end to work.
If I read a story in a collection which had a cliffhanger, and the rest of it wasn't in the same book, I would stop reading and not bother with that author again. Such a stunt shows extreme disregard for the reader. I would also seriously question reading anything handled by the editor who thought it appropriate. Novels I really like will have me waiting for a sequel (though I tend to wait for a complete set before starting a multiple book series) but for a short story with no guarantee of resolution unless I wait for another collection is just ridiculous.
TV shows are often critized for doing cliffhangers for multiple-part episodes after which everything goes back to status quo. There has to be a reason to care what happens after the story is done hanging. Gimmicks to sell incomplete maybes just turn me off.
"Yes, you will get the rest" is key for me. "Turn the page, wait for the fall, wait for next summer" are all do-able. "Maybe, if this goes right, but we have to figure it out first" is the mark of a child trying to use a trick instead of mastering the fundamentals first.
Books, novels, short stories, screenplays (movies), plays (stage), and teleplays (screen) are each their own beast with their own rules. However, they all fall under writing, which too has rules--that can be applied to every form. And subsequently applied to their separate genres.
Cliffhangers do work, but they have to be used right. People clamored for the above movies I cited, even after their allegedly disappointing middles. But writing them in tv shows or stories where the conclusion does not have a guaranteed airing or printing is dangerous and often backfires. Timing is crucial but so is follow-up.
Their actions in the plot should reveal their character. If character one sees a spider and faints, then I know they are afraid of spiders. If they are up against insurmountable odds but shout 'Maybe today is a good day to die' and lay about with their sword, that tells me boatloads about them. 
