It's not that they're particularly rich, as far as rich people go, it's that the neighbor is like, the chief of staff for the Senator who's in charge of the committee that sets the FBI's budget. Imagine you're a low to mid level employee of a company, and you go do something that makes all of the CEO's friends, business partners, and investors pissed off at him. Do you think that's going to be good for you?
After all, maybe I make $300k a year and think our mayor is, by the standards of politicians, one of the good ones; and getting invited to fundraising dinners and charity galas and rubbing shoulders with influential people makes me feel important and successful. So maybe I'll donate a few thousand dollars every election cycle.
On the other hand, maybe you make $300k a year but think political donations are a grubby embarrassment; that fundraising events are full of fools, the stuck-up and the self-important; and that the two parties produce policies that are barely worthy of your vote, let alone your money. So you don't donate anything.