Just because it isn't perfect it doesn't mean it's useless.
Just because there is no way to stop 100% of all crime it doesn't mean taking measures to reduce crime is futile.
There is a lot more to this than just blocking the site. It will also change social norms. Right now, if a 14 year old as social media, nobody bats an eye; but with the 16 year requirement, through all the sudden, parents aren't too comfortable with letting their 14 year old have social media. So not only will they need to find some free VPN totally not spyware to use (and even know that that exists and how to use), they will also have to hide it from their parents, as it is no longer socially acceptable for 14 year olds to have social media.
And before you say "Kids can easily get a free VPN and hide it." Never underestimate tech illiteracy.