He's barely played because the current style of gameplay doesn't allow it. Why play Alistar to give a little disruption, but add no damage, when you can play Amumu, Galio, Shen, Rammus, or Blitzcrank, cause the same amount of disruption (or better), and actually deal damage in the process.
Not to mention the vast majority of players want one thing: Lot's of KILLS!!!! KILLS WIN! If your K/D ratio is positive and full multiples of 2+, you're winning! Unfortunately for many others, this is the wrong focus to have, because kills don't win games, towers and the nexus do. Alistar is very effective at taking down towers, and in that respect, can win games... if every time you make a push you take a tower, you're doing pretty well, even if you lose the teamfight that ensued there.
The problem is that Alistar is actually a tank by the definition that he is incredibly hard to kill, and as a balance, does little for damage. All the other tanks are slightly easier to kill... but do a metric ton more damage in a teamfight. I still believe this is a fundamental flaw in the game as a whole. A team full of tanks can win games, simply because they outlast the squishy, more offensive built enemy. Gold for gold, the tanks will win, because they still dish out more than enough damage, sans any purely offensive items.
In my opinion, Alistar's greatest strength can only be accomplished with Flash, Pulverize, Headbutt... and then he goes and beats on the tower until the teamfight is over. Good Alistar players usually accomplish this well, but you always have to ask yourself if one of the other, more damaging tanks, would have done the job even better.
I think he either A) Needs a complete rework to become less reliant on flash for initiation. or B) Needs his damage output brought nearly up to par with other tanks, and as a consequence, have his survivability slightly nerfed.