The main reason I’ll be choosing classic over BFA is server community. Being known on your server, knowing other names on that server. Knowing who the best Enchanters, LW, Alchs etc all are having them on you’re friends list for future work.
Fearing that certain name on the opposite faction when you see them out in the world lol. Forming groups for quests, dungeons exploring actually seeing people in general while your questing will be good actually.
Community is everything in an MMO to me and retail has lost its community with all the ease of access features, crossrealm & sharding.