I think thats because those full pvp/loot MMOs are more fundamentally reliant on that old timey environment where you have no centralized information regarding the game itself along with optimized ways to play, alongside the form of the game itself being novel enough to make people want to play even if they are accomplishing little.

"Theme park" MMOs or whatever might have started in that environment but they could adapt to it even if it caused toxicity and friction in specific areas.