Not everyone may know or remember this, but neither Twitter nor Facebook were built on the paradigm of selling user data. That came later.
@plsburydoughboy Paid accounts would kill any major social media platform. Even a Mastodon instance with paid accounts (if that's even possible) probably could not stay profitable.
@plsburydoughboy LinkedIn is a bit different and to just use the site you do not need to pay. My understanding is that the paid LInkedIn features are things like InMail.
@skquinn Twitter would have applied paid accounts the same way
@skquinn It worked for LinkedIn