It is either an extortion from your domain registrar or sometimes opportunistic domain squatters taking over your domain for a year or two. Check for how long it was registered a put a reminder to get it back

Surprised a boring platform like LinkedIn has that many users.

It is to be expected. most people who migrated early on did it as an act of boycott, and not because they needed an alternative to reddit. so when the boycott failed, the natural thing for them was to go back to the plateform with the bigger userbase.