The main reason in relation to the "why" could still be that those users are completely oblivious to the degree of inaccessibility of their content. It's acces

The main reason in relation to the "why" could still be that those users are completely oblivious to the degree of inaccessibility of their content. It's accessible if you are logged in (and extra requirement on mobile: app installed). If not, it probably won't load or at best will be behind a barrage of popups nagging to agree, sign up, etc. There is no point in joining either, twitter is for people that already are heavy users and have a network, or celebs. For new users it's dead.