I would love to write something "important." I think I had a great start with a novel that was much too long for the point it needed to make, and I didn't know nearly enough about writing at the time to pull it off. I still might not know enough, but I'm getting itchy to resurrect that project and give it another go.
"Social" writers have always been passionate, so that's not the problem, and every cause has a loyal group of fellow enthusiasts/activists, so that's not the problem either. The problem is the public is notoriously fickle and getting a large number of people to care about an issue is tough. You have to hit them just right with just the right message delivered in just the right way at just the right time. An issue gets ignored one year but then is all the rage the next. Even those who say "I've been saying that for years and here's the book to prove it" get ignored in favor of the hero of the week. Welcome to celebrity; it's not likely to be any different any time soon. Anyone who could predict these trends would be able to change the world and make a ton of money on book sales in the process. Therefore, write for the passion and see who responds.