re: WoW

Nostalgia is a small part of it. The game's mechanics were deeper and more interesting. Players were forced to make difficult choices and gearing was hugely rewarding due to the end game structure.

Classes had actual identity and higher skill ceilings. Sharding, layering, cross-realm play, etc, were absent, resulting in tighter communities.

I had about 100 hours on Nostalrius. Nostalgia brought me in, the superiority of the actual game design is what kept me there until the server was taken down.

Asmongold made a video on the problems of modern WoW and why these changes have resulted in the mass exodus of players.