They do[1]. Most social media sites in the US don't allow children under 13 to use their sites, as a matter of policy. There have been proposals to expand COPPA to other forms of tracking and to children under 16.
To be clear, “age checking” involves nothing more than having the user enter their birthdate via a datepicker. Not exactly the same kind of verification used for things like cigarettes or alcohol.
Right. The alternative would be mandatory identification to websites, which would be a gross violation of user privacy, and impossible under the US’s current ID schemes.
You can use parental tools to disable these apps. Demanding thar whole world uploads private IDs to sites to check age because you refuse to parent well is absurd.