Several comic lines have explored this issue. It's always come down to the fact that there are people just as rich as Wayne who are corrupt and bankrolling mob families, drug traffic, providing weapons, lobbying government, etc. Essentially it is one billionaire against a dozen billionaires. So, he still has to don the bat suit to do illegally the shit he can't do legally. Often he ends up using intel gathered as the bat for rich-people power plays to oust other corrupt rich people.

I think it's poignant of real life. If you want to stay rich, you don't fuck with the other rich people, because they will disappear you faster than you can blink. Being rich is a club that you are only part of until you start fucking with other people's wealth. If you are an ostracized solitary sod, who doesn't go to any social event and all you political stances are openly hostile against the entire rich class you are a part of, you won't stay rich for long and all the power that comes from that wealth will disappear, if you get to keep your life at all. Without all his money, Batman is just a really buff dude who is very smart and knows martial arts. I've met a few of those. Almost all of them broke as fuck.