It’s incredibly easy to see these changes as Google clamping down on ad blockers to protect its monopoly in online advertising. I don’t think that’s necessarily the case: Google knows as well as I do that a total crackdown would give governments like the European Union and United States more ammo for antitrust lawsuits. It would also be a motivator for more people to switch browsers, which would weaken Google’s browser monopoly. The stated claims about security benefits also make sense…
If Google wanted to crack down on adblockers without risking an antitrust lawsuit in the EU, they might look to introduce features that undermine adblockers as a plausibly unintended side effect of some other valid goal, like security. That’s what this looks like. Without access to internal communications no one can prove that Google intended the effect on adblockers, but it’s certainly convenient for them, while plausibly deniable.