I feel like it is because of the things people consider mistakes. Like imbalance(faction,class,spec,prof), horrendous travel time, annoying quests, many endless grinds for minor payoff, gear and resource competition.
When you think about the history of video games, they are fairy recent inventions.
I would posit vanilla wow (Era) is probably one of the best games ever made, if not the best game.
I would not be surprised if in the future Era has more active players than vanilla (or wotlk) ever did at their peak.
Blizzard just needs to master Era season (without changes, on 2 year cycle) and market it to new audiences. The game is super enjoyable and welcoming to new players.
This reminds me of D&D. Many of us play a version from 1981 (Basic/Expert) not one of the later or current editions, because B/X is a classic masterpiece.
…WoW has more development time put into it over those 20 years than any game ever made.
There’s been big milestones that’ve reshaped the way the game is played, including Dragonflight.
The best argument I’ve heard against Modern WoW vs. Classic is Modern feels like an ARPG instead of an MMO. You play in instances and chase a far more rigorous loot grind compared to the original game.