I would add also WoW to the list.
I had friends that after a while would connect more to socialize than to play.
And probably the equivalent in the 90s were MUDs, although they were text only.
I played with people on WoW who are still good friends who are now in high places. It was truly a generation thing. Like I watch Stranger Things and I think, I wish I was on the internet before the WWW with BBS, and with walkie talkies, maybe not so much the smoke demons, but then, during my teenage years it was WoW and that was a very special time for me.
I couldn't do it now, I've changed, the fabric of my mind has changed so that it just wouldn't appeal to me now, but back then it was great.
Would I want my son doing the same? 20,000 hours on a game over five years? Yeah I'm going to say no, but, things are different as a parent.
Oh man, I have similar statistics for the MUD I played, it was insane.
However, the thing I found most fun about that was programming plugins to take the chore out of various tasks, so at least it helped me in that I had countless hours of programming practice.
Otherwise, my experience was the same as the GP's, I have many friends today that I met fifteen years ago on that MUD.
Easily. A lot of that time was probably spent mostly AFK doing other home stuff, watching series, reading and what not but I can relate to that played time. My character almost hit four digits days played before I ended up letting my subscription lapse after realizing I never logged on wow anymore.