Too many stupid Alis that blow their cc on someone unimportant like the support while their carry gets mopped up.
Wish more people would realize Ali's potential as a dedicated peeler. "Oh, you want to dive my carry? Too bad, I'll just headbutt you into a wall. Then Pulv you when you come back. Then headbutt you again." --- >;_;> >;_;> ^_^>(::) . . | GT:TwinInfinite He took our cookie... | Active: LoL, TF2
Because he requires a bit of skill and thought to use. We all know this, but the average player is bad. Alistar has lots of room for bad plays because of headbutt, I've seen so many bad headbutts. Likewise, I have seen many failed pulverizes & players who ult on Alistar RIGHT BEFORE HE DIES. Oh yeah, and he isn't safe, he has no ranged skills unless you count headbutt but that can put him in a bad spot and his enemy in a good spot.
tl;dr - He isn't braindead like Taric. --- Oh no! It's Idiot power!
He's one of the two free champions. He's very fun, and fairly straight forward (even if there is a decent amount of skill possible to use him to his full potential). He also has a reputation of being broken. All these things together make him a perfect candidate for being picked often by people who aren't at a high level in the game skill-wise.
When someone is seen as braindead easy, but also a great contribution to the team, why would you not pick him if he's an option? (there are plenty of reasons, but obviously a lot of people don't know them) Any time someone is always banned or taken, people feel they need to jump on that chance. But if you just use him to peel and initiate, and don't pull off any great plays there are far better options.
http://www.youtube.com/watch?v=Wb5NlNuUupU sums it up in general. --- Gt-fullmetal9yanal I hate most of you. This has been entrusted to me. http://i259.photobucket.com/albums/hh291/sly_reflex/trollomen.png