The first hit is free
Twitter has probably realised that the drug-pushers' tactic of free samples to get people hooked then charging through the nose (sorry) doesn't work where new suppliers are popping up all the time, all with similar free offerings. The business won't survive if it can't create revenue and as people are highly unlikely to pay for Twitter it has to be funded by other means.
I wouldn't let him tweet or Insta or Watts anyway, but my eldest mainly communicates with his peers by plain old-fashioned text message or closed Snapchat group. People who need to communicate with us in a manner not appropriate to a text message, email or - you know - a phone call - use Signal.
Who remembers Geocities, Friends Reunited or MySpace these days? Who still regularly posts updates to their non-corporate Facebook front page? Twitter may not disappear but I suspect its days of being the ubiquitous channel for shortform communication between 'ordinary' folk are over.
I think slightly different rules apply to YouTube due to the sheer quantity of hardware required to make the thing work making breaking into that market extremely expensive but a mainly text-based service these days doesn't require CERN levels of investment.
Another one will be along in a minute.