I really, truly think it's just that he...
- Wants to get his friends work. Kevin James couldn't get shit after King of Queens, so Sandler used his connections to get Paul Blart done. That made money so it got a sequel. The same with Rob Schneider: couldn't get work, got four movies with Sandler: The Animal, Deuce Bigalow 1+2, and the one where he switched bodies with a girl. He's even done if for David Spade and he doesn't even LIKE David Spade. I mean... JOE DIRT is getting a sequel. I -like- Joe Dirt and don't think it deserves a sequel.
- In order to help produce those paychecks for his friends, he has to put out drivel for the studios. Some of it (Hotel Transylavnia, 50 First Dates) is decent. Most is crap. But he has to do this shit to keep relevant.