Seeking political office is asking for punishment. The media can be brutal. A small slice of the general population will be haters no matter what and in absolute numbers that's a lot of people that hate you.

Billionaires can insulate themselves from this brutality and may have some experience with it already. Non-billionaires can't, and so it's just not worth it to run for office unless you care more about power than about yourself and your family.

Not saying that billionaires are great politicians or anything, but it certainly makes sense. If we want something better we need more civilized discourse.