Because it's literally their job: Protect the citizen. They may not do a good job all the time, most times they are even very bad. But nonetheless do they try and prevent most of the worst cases. And TikTok is so insane efficient in what it's doing, the line between benefit and harm is so thin, it could easily turn into a "worst case"-scenario if people don't observe it careful enough.
That is not automatically the government's job. At least not in every worldview.
And these things exist on a spectrum. Protecting people from direct external threats is pretty unobjectionable to most philosophical systems that allow governments, but there's a lot more controversy around protecting people from themselves.
As someone who thinks Unrestricted Warfare is one of the most brilliant books I have ever read, the idea most have not read this book in the US military is quite laughable.
Imagine people having no issue with the Soviet Union delivering a free daily newspaper to US teenagers in 1960. The level Americans have their head up their own ass is unbelievable.