I mean, isn't one of the key points of twitter to get teh most followers?
yes, but twitter account can rack up millions of followers without anyone knowing who is behind the account.
Well what is the point of that? I ask as the dad of someone whose life goal was once to be a millionaire YouTuber.
many people want to keep their online anonymity. being "outed" as the person behind an account can, potentially, have consequences ("wait - for years now i've been following the musical recommendations of some long-haired government-employed 50-something suburban dad?? UNSUBSCRIBE!!!").
youtube is different. for the most part, wannabe youtube millionnaires/influencers/asshats appear in front of the camera, so at a minimum you see their face - that's one aspect of anonymity that's lost. you don't have to disclose your identity and you can hide behind a non-identifying account name, but anyone who gains popularity will inevitably be identified/outed.