This isn't just your world, meticulous planning, even with preparation to be fluid is often worse than pure improv. When your players know that there isn't much lined up ahead, they start to contribute lore and tone, and they seek adventure instead of reacting to it. Players may be enjoying a TV show, book or game at the moment and want to echo something they enjoy, either a character or even just a vibe, oftentimes a game that encourages that to come forth is more fun.

I have a beloved campaign setting that between last time I used it and now, I've made thousands of changes and improvements and I'm truly excited to run it, but after I next run it, I'm going to shelve it indefinitely until running it for my children one day, if I have any. Instead I'll just sit down in session 0 and ask people what tones and fiction touchstones they're enjoyjng, and then build the setting then and there with them, vetoing options that I'd not enjoy running but keeping things open. From there, I'll encourage them to build the world with me, a player will care more about the kingdom they named or the wandering superweapon automaton that they suggested than anything I could come up with, not because they're better writers but because people do just care about the things they enjoy more.

It's like when players are overly invested in their own backstory over the plot, it's not because your plot is bad but because they have daydreamed about that and are keen to explore it above all else, not all players love to make a complex backstory character but the majority who won't may still enjoy collaborative worldbuilding and be excited to explore the parts they build, as a GM your role is to keep things concise and develop the through line that allows all these factions and locations to shine, while even keeping that flexible and casual.

TTRPGs are often about escapism and having fun often outweighs having something meaningful, players will remember the session they smiled through more than the session with well achieved complexity or good writing. Get those dice off the shelf and have another go, and remember to have fun first. It's always fun to build your setting and story, and it's a great way to enjoy this game away from the table, but your players don't share in that enjoyment, and if you need them to have the most fun for you to have fun too, then remember that the times you have fun daydreaming about your world without them are moments that may be fun to have together.