I agree it does happen, though the party system really limits the possibility. It keeps nationally popular but not moderate idealists like Ron Paul and Bernie Sanders sidelined and picks winners long before primaries in local elections.

I live in a state with caucus primaries and it prevents any non-party candidates. Even at the local level you get some horrible choices of picking the least bad, corrupt, or even crazy guy.

Luckily, for at least some positions there is not enough party interest and there are 3 or more candidates that have to explain their platform and reasoning. If only that was the case with the more important positions.