People buy things because it provides them value. Increasing buying means that more value is being delivered to humanity. Advertising makes the world a better place.
Weird thought: if advertising is misleading harassment, perhaps it doesn't even increase consumption overall, but only consumption of the things being advertised. Perhaps people would buy more, from the market as a whole, if left in peace and given impartial advice about products only when they seek it.
Because advertising works. Full stop. It doesn't matter if it is valuable or not. It just works. Definitely not with P(buy this crap) = 1. But the effect is still there and real and measurable and google has made colossal amounts of money out of exploiting it.
It might as well be a magic spell. You show the user the thing, and they buy/subscribe/click-through with some probability according to massive ML model that knows everything there is to know about them.
Yes - people are capable of making decisions in their own self interest. But there exists a gap where not _all_ of peoples' decision making process is the aforementioned. And that gap can be exploited, systematically.
The existence of that gap is the actual problem. At scale, you can own a nontrivial quantity of human agency because that agency is up for grabs. Google / similar make their money by charging rent on that 'freely exploitable agency'. Not by providing value to people. The very idea is ridiculous. Value? How are you going to define a loss function over value?
ML models on click-through or whatever else don't figure out how to provide value. They find the gap. The gap is made of things like: 'sharp, contrasting borders _here_ increase P by 0.0003', 'flashing text X when recently viewed links contain Y increase P by 0.031', etc and so on.