Isn't it a simpler solution to create some protocol for a browser or device announce an age restricted user is present and then have parents lock down devices as they see fit?

Aside from the privacy concerns, all this age verification tech seems incredibly complicated and expensive.

I think this solution exists (e.g. android parental lock, but also ISP routers). But parents and industry have failed to do so on a greater scale. So legislation is going for a more affirmative action that doesn't require parental consent or collaboration.

A service provider of adult content now cannot serve a child, regardless of the involvement or lack thereof of a parent.