Part of the point of so many of Batman’s villains is that, to quote joker, it’s not about the money but about sending a message. Or holding power in many cases. Many of the most corrupt villains are not only bankrolling bribes, they are also blackmailing tons of people and many more live under threat to loved ones. Wayne just waltzing in and saying “I’ll pay you triple to be good” does nothing. Because if they don’t do the villain’s biding they will get murdered and their family will be slaughtered. Hence the need for a vigilante to disrupt the corrupt system with direct action. That’s the whole arc of Harvey Dent, for example. The system took him down in the worst possible way to shape him into another morally bankrupt psycho.