"Sure, you can use my wifi while you're over. Just enroll in MDM real quick".
As brought up in another thread on the topic, you have things like web browsers embedded in the Spotify app that will happily ignore your policy if you're not doing external filtering.
There's nothing technical stopping device manufacturers from making this easy for parents to do. They choose not to.
Fair point.
I guess it (network-level filtering) just feels like a dragnet solution that reduces privacy and security for the population at large, when a more targeted and cohesive solution like client-side filtering, having all apps that use web browsers funnel into an OS-level check, etc would accomplish the same goals with improved security.