With enough anecdotes, that 100 billion dollars starts to smell like click fraud. Google owns both sides of the ad market and is less than transparent with how their ads perform or how bids are calculated.

I will be very curious how the promoted stuff works with LLMs. When you ask a LLM what the best brand of shoes are, can folks pay to influence the result?

I personally know people spending 6 figures at the minimum on SEO, because they see huge conversion rates for their own businesses (which are not web-based stuff by the way, more of a niche in person technical services).