Because children just click through the age gate when it suits them. With this legislation, a parent that purchases the device and creates an account for the child can set the age once and take the decision out of the kids hands. It's a huge improvement without any significant privacy issues. I can't fathom why the tech crowd is having a collective aneurism over this.
>OS isn't the thing displaying content
But the account on the OS is the right place for the single source of truth of properties of the current user.