The answer is not complicated, and the logic on this board is strained by people I think that don't work in marketing.
1) Advertising works.
2) Coke, a sugary drink, is largely kept alive by smart marketing, that involves mostly advertising in the end.
3) Much of advertising is quite wasteful, because it is a fuzzy instrument - but on the whole, good marketing works.
4) There is a lot of self-awareness in the industry on this, and no doubt, a lot of borderline fraudulent actions by participants willingly spending money they know doesn't work.
5) Ad networks will happily sell you ads that don't work, and look the other way when there are shenanigans.
The problem here in the thread, is that people are having a hard time grasping how all of these things can be true at the same time, but it's not that hard really.
That some ad spending turned out to be 'not useful' is 'not news' when everyone knows that easily 50% of ad spending is probably wasted, we usually just don't know which 50%.