It seems unlikely that "is user adult" is not already easily modeled by any of these companies to within a very high degree of confidence. Even 15 or 20 years ago Google search could bracket your age pretty effectively. It doesn't seem like this adds metadata that wasn't already there.
Except that in the legal sense, "is user adult" flips from false to true overnight, and there isn't an easy way to account for that in any model that doesn't include verified ID. Same reason many liquor stores ID anyone who looks younger than 40.
The official app/client is 100% legally compliant in its unmodified state. But doing something like using another client, having your PDS say you're age verified, or using a ublock origin rule to change where the geolocation API thinks you are completely sidestep it.
It was never going to be perfect. I suspect the goal with things like these is to add additional friction to the process, to make it much harder for the general population to bypass them.
