For the lore
It's co-op, i can customize my character, and I can invite more and more people to play with me if I want to.
Oh, and if the gameplay is good, i know there will be more stuff to do.
That's a good point. I played Fallout 4 for a long time until I realized that I was just playing by myself, and nothing that I did really mattered. In an MMO you have actual friends to enjoy the game with, and witnesses to see your progression.
Doesn't anybody else end up playing a solo-RPG, even in the one of the biggest MMORPG's in the world, though?
I don't play MMORPGs anymore. I'm actually sick of MMOs in general by now. Too time-consuming, actually anti-social rather often than not, all games using the same obvious mechanics to keep players hooked (like drug lords), no innovative gameplay for over a decade. We've seen all of it.
I'm back to Singleplayer and direct LAN/Online Multiplayer games with friends where I can set the pace as I prefer. E.g. grand-scale strategy games and war games - both real-time and turn-based.
#MakeBlizzardGreatAgain
I like MMORPG's because they appeal to all sorts of different gamers. I'm a WoW player myself and a rather new one at that. There are so many different ways for people to play. I prefer questing and immersing myself in the story. I know that others live for PvP and raiding. Also, I love the wide variety of landscapes that the map encompasses. Furthermore, I like the fact that it is nearly impossible to reach the "end of the map." The endless possibilities of MMORPG's is what I like most.