You're not missing anything. You got it right. The entire funding model for tech is destined for a financial collapse that will make 2008 look like child's play.

https://www.fsgoriginals.com/books/subprime-attention-crisis

From the unreliability of advertising numbers and the unregulated automation of advertising bidding wars, to the simple fact that online ads mostly fail to work, Hwang demonstrates that while consumers’ attention has never been more prized, the true value of that attention itself—much like subprime mortgages—is wildly misrepresented. And if online advertising goes belly-up, the internet—and its free services—will suddenly be accessible only to those who can afford it.