I don't suppose you could have asked your question, if you were genuinely curious, without being insulting in doing it?
Because some of us vote on more than ONE issue. Also because some of us vote for the person, not the party.
I'm not a liberal and I'm not a conservative. Libertarian comes closest, but even then it's not a good fit.
Think of it this way: I may decide to vote for someone who is not gun friendly because their positions on other issues that I care deeply about are strong and they have good influence in those areas, and because their opponent(s) have positions on those issues that I find abhorrent and they are not particularly strong on gun rights. So I vote for the non gun friendly person. And I make sure that they know just how important gun rights are to me, along with the other issues. By doing that, I can influence their position. Who knows, maybe I've made them less anti-gun than they would have been otherwise. Far more of us are more middle of the road politically than are folks who are on either extreme of the political spectrum.