Because I would rather parents make the minimal effort [1] to restrict which pages their children visit and how often, than legally require every website and game to deanonymize, surveil, and censor their users. Which includes not just Facebook, but every forum (HN, reddit, small bicycling pages [2]), game, and chatroom. Because the latter would mean anyone hosting public discussions would be doing so only at the government's will. If they don't like the direction those discussions take, they will use the vague laws against "harm" to force a change. Like the UK government admitted [3]:

First, we are told, the relevant secretary of state (Michelle Donelan) expressed “concern” that the legislation might whack sites such as Amazon instead of Pornhub. In response, officials explained that the regulation in question was “not primarily aimed at … the protection of children”, but was about regulating “services that have a significant influence over public discourse”, a phrase that rather gives away the political thinking behind the act.

[1] It's not minimal now, but that's the point of government funding and requiring better parental controls.

[2] https://www.techdirt.com/2024/12/20/death-of-a-forum-how-the...

[3] https://archive.md/2025.08.13-190800/https://www.thetimes.co...