I think it was similar to all the early MMO's. They were a platform to create a community in a time where that was hard to do in the real world. Back when I started playing Asheron's Call there were basically two "nerds" on my school of like 1000 students and the town computer club had 5 members. It wasn't like today where you can easily find someone to play DnD or board games with and you couldn't really play video games online. Hell, how many people under 35 knows what the internet chatrooms were?

MMO's let you go online and be social and build communities. WoW did that really well back then. Eventually as things went on, MMO's got more and more tools that let you avoid building those communities. Like the dungeon finder in WoW. I think a lot of MMO's and games in general turned to letting peope get their dopamine fix from increasing numbers through RNG rather than being social.

I know people who stuck around with WoW because of the social communities they build. One of the guilds I was in 20 years ago still meets up in the real world, I know because one of my old friends still plays. I also know people who stuck around because of what is essentially the idle gambling. I became a jock of sorts back around the burning crusade release because I had to put a lot of focus into water polo training. Which meant I didn't do a whole lot "nerdy" stuff for a decade. Once I started doing "nerdy" things again it was easy to find people near me because everyone is a "nerd" these days.