Well, let's take some of the more controversial metaplot changes as examples.
The Spellplague, the big event for Forgotten Realms going from 3e to 4e. . .they advanced the timeline over a century, killed off most of the gods, completely re-drew the map (to the point of adding a new continent, and wiping some countries and some of the most popular cities literally right off the map), completely re-wrote the whole planar cosmology, changed how magic works, and changed the tone from a fairly typical Tolkieneseque traditional fantasy world into a grimdark 4e "points of light" setting. . .
That's not "having more information which may inspire you". . .that's a whole different setting, with a totally different flavor and style, shoehorned into the old setting.
Or take the 5th Age in Dragonlance, a similar event that took Dragonlance from AD&D to a newly created "Saga System" of a card-based roleplaying game. . .that again advanced the timeline decades, caused every god in the whole pantheon to disappear, completely rewrote the rules of magic, changed the lore around dragons entirely, and again took a heroic, traditional fantasy setting and completely changed the tone to grimdark.
From a longtime fans perspective, they essentially ended the setting by changing it so much that any new material would be completely incompatible with anything that came before.
Also, it's NOT as easy as telling players you're doing things differently. . .for a fair amount of players, a game that substantially and intentionally violates canon is abhorrent. They have their mental picture of what the setting is like, of what they want to imagine when they play the game, and something that is like it enough to remind them of that setting. . .while at the same time being different enough to stand out, is mentally uncomfortable enough to make them not want to play.
(You're also assuming the 5e-ism of "session zero" is universal throughout gaming, this isn't just about 5e, it's about RPG's as a whole)