Apple is a closed ecosystem, multiple users feature is a opposite of that.
For example, it's hard to manage app store purchased Apps if it's easy to switch users in iPad. It's hard to manage iCloud sync when switching, it's also related with privacy.
I would not be surprised if Apple fully commit to the one person per portable device scenario for privacy and CSAM laws.
It would solve the age verification challenge by tying a device to a person. Since they can, I think they might.