He / Him
I think there are just different styles of DMing. Some like to spend time fully detailing their world, others find joy in building it "live" during the campaign.That's why you shouldn't establish too much information. You can't--even in principle--establish everything. Establish only what is needful, what is useful, and keep loose and flexible with the rest.
Only if you try to fill in every inch of the map. You might be surprised how liberating it is to, as they say, "draw maps, leave blanks."
Why not? I'm genuinely curious. I do this all the time, both because Dungeon World tells me to, and because I enjoy doing it. Sure, a lot of the setup came from working with the players, but (for example) the good-guy thieves' guild organization, the Silver Thread, only came into existence because the Bard said that's the group he ran with back before his family got their big break.
As long as the expectation isn't incredibly over-dramatic, it's almost always possible to get it in. Yes, the player should have realistic expectations, but "realistic expectations" is a very weak requirement in most cases.
I'm definitely a blank map DM. I usually figure out the starting location and a few key features of the campaign world, and then fill the rest in as we play. During Session 0 I'll plop some guild halls, temples, or cities onto the map based on character backgrounds or backstories. I really enjoy the collaborative, improvised feel of building the setting as we go!