Fun fact: WotC hates goblinoids. The bugbear and its current +1 LA are a fine example of that.
Bugbears already have 3 humanoid HD, which is about the worst kind of HD one could have. In return for this they get decent ability bonuses, a small skill bonus, scent and natural armor. Pretty much all of these are done better by other creatures. Even the few goblinoid-centric feats aren't a reason to become a bugbear, because they could be just as easily taken by a goblin or hobgoblin.
Bottomline: sometimes you don't need a lengthy explanation to justify your decisions. Bugbears are weak, but giving them -0 LA is all I can do here.