Elections are important, but they're just one part of the political system. A lot of machinations and politics occurs outside the scope of elections or even of the public eye.

Money doesn't just buy ads. It influences the decision of who is a candidate in the first place. It buys operational range. It pays salaries for the right friend of X, the right family member of Y, etc. It buys other bribes, etc.

Consider watching this: https://www.youtube.com/watch?v=qnOmUWd-OII