Personalization came along in MMOs around the same time, and it was hard to communicate the difference to people between a persistent MMO zone as a "place" where people and things exist, even if those things are inappropriate for your character or hostile to the point that you can't survive there or too crowded for the intended flow... versus an instanced MMO zone, a little pocket universe for you specifically that has no strangers in it, which is more of an "experience" or "cut-scene" for you to imbibe prepared content.
A heavily instanced MMO may as well be a single-player or co-op game with a shared chatroom as a lobby, there is absolutely none of the emergent play, none of the characterization of players & groups of players, nothing original. Instead, give me the same ground to walk on as everybody else, even if our tread wears all the grass off of it; Half of my life in these games was getting bored waiting for a mob to spawn and fucking around making friends waiting in line, or ganging up on the guy who wanted to cut in line, or waging war on the clan that currently controls the needed territory, or grouping together to fight mobs higher than I should be able to hit (which the instance will just Adjust Downwards). Instancing and other auto-personalization algorithms cut the annoyances that are central to human socialization, achievement loops, and wayfinding.