"Yeah, I'm getting these paybacks from companies, but I do it to support my campaign, else this scoundrel, my opponent would have gotten elected, who would have voted for very bad policies".

Besides, long term, the system self-selects against too much morality. If they can't trust you to keep your mouth shut and play the game, you wont get the support you need to get to the next level.

The one willing to put up with everything and anything, either participating, or keeping their mouth shut and pretending to be above it while still allowing it to happen, becomes President.