Why can't Apple's Screen Time blacklist certain URLs?

Apple devices come with a feature called Screen Time that can be used to put parental controls on a device, and it can also be shared across all devices that share the same iCloud account.

The feature I'm most interested in is the ability to blacklist certain URLs, which can be found by going to Screen Time --> Content & Privacy --> Web Content --> Customize.

But this only works for Safari -- obviously a person who wants to defeat this feature is just going to install a different browser.

Why can't Apple just adjust /etc/hosts at a root level?