You’ve nailed the first two stages of enshittification in your story there. Stage 1: bring in users with a genuinely good product they like! Stage 2: once users are locked in, prioritize your business customers (in this case, advertisers) and make things continually worse for your users.

But stage 3 is just as crucial: once the advertisers are locked in, make things worse for THEM just for your benefit. That’s how google makes such obscene margins on adverting. Publishers and advertisers would love an alternative - but google has done an excellent job of preventing that through unlawful monopolization tactics. Hence thus case, and why it’s so important.