People find him funny because people USED to find him funny... like, twenty years ago. See Billy Madison, Happy Gilmore, and the Wedding Singer. Now those teens who saw those movies have kids of their own... and you can see how he's chilled out along the way. I don't have any kids myself, but I still find Big Daddy to be absolutely hilarious, because when I was in my 20's, that's how I expected I would act if ever in that situation. The Longest Yard was really well done. And Little Nicky, well. It's 100% ridiculous, and that's why it's funny.
I mean, Adam's now pushing close to 50... and yet his movies... well... they're still relatable to we who grew up with his style of comedy, and even offer some roll-over yuks to those folks who have kids.