Easy: none of them have a chance of winning.
Third parties are (unfortunately) a joke - and I refuse to vote for "the lesser of two evils."
Show me a third-party candidate with enough support to even be admitted to the debates... if I knew how to help make that happen, I would!
The system is utterly corrupt and broken.
I suppose I could vote for Donald Duck, but what purpose does that serve besides proving to people like you that I'm not lazy?
I'm not asking anyone to agree with my position -- but could you at least call me a cynic instead of a lazy bum? I made a conscious decision not to vote. It wasn't because I was watching TV instead.