They depend, though, on having enough personal and behavior data to accurately predict your behavior. Then the algorithms refine themselves by feeding you information and testing if they managed to get you to behave in the desired way.
Just keep testing and refining with enough data and enough people and voila, a democracy where the votes can be bought in large enough numbers that the results can be, too.
Remember, it's not just the ads. It's the content they're choosing to show you. Notice how platforms are moving away from chronological timelines to one's with black box methods where they choose your timeline items you see?
The weak point of this system is that it needs a constant flow of information about what you're thinking and doing.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!