Why not?
Because there typically isn't much to fight over. For example, I'm voting for Duke Aiona for governor. He has an opponent, but will likely get more than 90 percent of the vote in the primary. I'm not voting for either Mufi or Neil Abercrombie for governor, who face each other in the primary.
The presidential primaries are a joke. They are so late in the election year that the nominee has usually been decided before the primary. They're talking about moving the date up.