>>715590029 (OP)Cultural and technological changes I'd say. Back when I first played MMOs, multiplayer gaming beyond couch co-op or hotseat was a sort of a rare treat for me, playing games online wasn't really something I did so MP was more like a LAN party thing or something we'd sneak in on the school computers. Then I hear about these games with massive online worlds where you play together with hundreds or even thousands of other people on the server and the appeal was huge and immediate. When I started playing, exploring the worlds felt amazing and mysterious, I'd go around being awed by what I found and often having no idea how to complete quests or beat strong enemies, which is where the multiplayer aspect comes in. I'd just run into random people playing through the same areas, we'd naturally talk about how to complete quests or make parties to kill things we couldn't kill alone. I'd help them with the things I had figured out, they'd help me with what they figured out and so on. If it went well we became friends and continued playing together, soon enough you've got a naturally-built group of people or guild to play with. It was great.
Things have changed nowadays. Multiplayer no longer has any special appeal in particular because it's ubiquitous. Exploring the worlds of MMOs doesn't really feel particularly unique since huge open-world games are common. What's even worse is the cultural shift. The kind of mystery and exploration combined with natural social interaction is just no longer possible, people nowadays just speedrun from objective to objective, the game needs to give them their GPS and they're going to follow some guide on YT too. If the game doesn't really cater to this, they just don't play.
The MMORPG golden years were lightning in a bottle, a creation of those times and of the culture we had back then. Now it's just something in the past.