I think the possibility of banning certain sites at least for minors is being discussed, after Australia set the precedent. But this of course has downsides, too, as some form of verification has to be implemented, that would almost certainly reduce anonymity and carry risks to personal data protection. A complete ban is unrealistic since people actually like to use these platforms. Plus, it would certainly entail massive political repercussions from the US government. This is already happening when US American companies are simply fined in the EU.