It has to do with probability.
The problem with this is that not all queries are made equal; not all books or queries have the same odds of succeeding. So probability has only a glancing relationship with each individual book's chances, because each individual book is different.
Some are guaranteed to never be published by a good publisher, because they're just not good enough. Some books are so good they're almost guaranteed to be published. And all books sent to a vanity publisher by an author with money to spend and no understanding of how publishing works are guaranteed to make it into print.
Most of the time, agents are (unconsciously) looking for particular characteristics in a query. The chance that your story will match any particular agent's interest is of course small. So, it makes sense to email many, many agents since the chance increases. A rejection could mean that your story or query was bad. But it could also mean that the interest was not lined up.
Good agents know exactly what they're looking for in the slush pile: a book which is well-written, and which they think has strong commercial potential.
It doesn't make sense to "to email many, many agents". That doesn't make your chance of publication increase: it just makes the number of emails you send out increase.
To improve your chances of finding representation, your best bet is to write a better book, not send your book out to more agents.
I am trying to start a query newsletter. It will basically have good queries. Then I email it to a number of interested agents. Agents like it because it will save them time and it would benefit authors too, I think, because they are exposed to many different agents. It is of course free for authors.
Would you be interested?
Don't use AW to pimp your services. It will get you banned for spamming.
You're welcome to put a link to your website into your signature, and I've allowed you your one thread to discuss your idea: but beyond that, you don't get to use AW to advertise your services.
I hope that's clear.