I think a comment I saw recently makes this make sense.

A lot of people have told me as you age, you get more conservative. I have not noticed this happen, but I think an entire generation did. Boomers. As they aged they had so many advantages the entire generation acquired things. Things they don't want to lose because they feel like they earned it. In some ways they did earn it (eg, pursued that promotion, bought that house after "a whole summer of working OT!")... they just don't recognize they started on third base and did not in fact hit a home run.

So if an entire generation can be as awful as they are, I think it must be a general glitch in human psychology. As long as you FEEL like you earned something, you will fight to protect it. I think that's what happens to billionaires. And aging republicans. There will always be exceptions, but I think in general humans will just tend to be this way.