Honestly, I think it's different people who dislike Brawl and Smash 4.
People who value the competitive side of Smash dislike Brawl, while people who value the single player side of Smash dislike Smash 4.
I think a lot of hate Brawl gets is irrational. Tripping is a game design flaw, but the other issues are not that big.
Yes, Brawl is slower than Melee, but it was designed that way. That the competitive scene didn't want something like that isn't a fault on the quality of the game itself.