Democratic Primaries

I think there are few such people who will not vote for the nominee (especially on DU). But it is an interesting question, even about those few, as to what their motivation is.

"not really caring about issues but just wanting to be on the winning team and getting your way" - the "spoiled brat" category? Maybe some. I think there are also some people who strictly are principled (and not pragmatic) in their decision making, who will not stray from their ideals, period. There are people who feel their one vote won't count anyway, and they would rather make a statement (or conversely, don't care strongly about voting to begin with). There are the extremists of various types, the anarchists, the survivalists, etc. who in some respects can be far left as easily as far right. (Libertarian and Progressive are not always at odds.) Less extreme, you still have the anti-establishment people, for who Sanders and Trump both had some appeal in 2016 whereas "mainstream" candidates have none.

Basically, there are probably a bunch of different answers. But it is a minority, regardless.