Well the reason Jackass became such a phenomena is a combination of things -

1) They do real stunts and put themselves in great bodily harm; whether that is being stupid or not. Jersey Shore crew's biggest threat is a trained stuntman coming up to them pretending like he wants to be in a fight.

2) They are genuinely entertaining people in of themselves. They aren't "acting" and they don't have to. Their interactions aren't funny because they're snobby whiny assholes who are oblivious to the world around them, they're funny because they're silly and relatable. You'll see this when they fall over laughing at a stunt/prank they pull on someone else.

3) They weren't making a lot of money when it started out. They started off as just a bunch of kids making videos of themselves doing stunts or skating videos. Thus, they actually in a way "earned" what they have now. Jersey Shore is just a freak show, where the actors have no redeemable qualities and made hay out of that fact.