I don't want to play a human in a fantasy game because I am one in real life. Gnome voices annoy me. In fact, gnomes in general annoy me. I'm tired of elves. I'm not at all interested in playing a blue skinned devil creature. Dwarves are cool. I would play one if they weren't forced to be aligned with all of the lames.
Orcs are awesome. Incredible Hulk. Trolls are great. Rasta mon. Who doesn't love cows? Undead that can take a beating and never lose a single body part? Sign me up. I just ignore the elves.
All of these are merely my opinions, but they are the reasons why I play or not play whatever I choose to play or not play.