Because the Republican in office was too weak within his own administration (McCrory). That's the only reason I can think of right now.

Right now Democrats are too passionately progressive. If there's anything we don't need leading good government astray, it's passion. It's good to question healthcare, equality, the amount we spend on the military, how nationalism can go bad, etc. It's bad to go out there with one solution and shout it from the mountaintops like it's the automatic answer.

Now I can't think of a reason to vote for a Republican either, but that may be a subject for another thread.