--If the independents outnumber Dems and GOPers, then why don't they vote independent? Why are there few independent candidates? --
Because the "parties" (I'll use the plural for your sake) have set such high hurdles it is darned near impossible for them to get on a state ballot, and if by some miracle they do, then they can't get in a debate. Cynical but clever.
What hurdles? All you've gotta do is collect some signatures from voters and pay a filing fee. And every candidate has got to do that.
An independent ought to have a better chance of getting on the ballot because he doesn't have to survive a primary.