The game world doesn't just exist. It exists to drive forward stories of the PCs (and explore and reinforce the theme of the campaign) -- and you need to openly establish constrains, reasons why these constrains are put and keep your vision clear.
Middle-Earth and Tékumel were created for languages first, and things like stories and games a distant second. Game worlds (such as they are) can and do
just exist (for a certain offbeat diegetic value of "exist"). And what's more, these kinds of worlds are the
good ones. They're richer and deeper than worlds created just for the sake of playing a game, or worse yet, created by committee. The sort of fantasy world that only exists when the PCs are looking directly at it, meanwhile, isn't just likelier to be shallow and incoherent; it's also more forgiving of
quantum ogres and other dirty tricks of DM illusionism.
The GM controls one or more characters in order to tell a story. Player controls one or more characters in order to tell a story. Can't see any particular difference.
The GM controls a whole lot more than just NPCs, and the aim of playing D&D, at least, is to have adventures, not tell stories.
The GM's sole authority over the game world was an important thing, but the hobby has grown out of it. Now it's widely accepted that worldbuilding is everyone's job -- players can and should introduce details, factions and locations, GMs can and should ask their players for input -- it's their game and their world too, after all.
Holy baseless assertions, Batman! The condescension is strong with this one.
(Just speaking personally, though, even if it's a tangent only, if
I sat down at a game table expecting to play some D&D and the DM asked me to introduce some detail into the game world? I'd get up again and leave. I wouldn't want to play with a DM who delegates the basics of the job.)