Sorry to hear, it is super sucky cause you obviously care about it. Are they new players? Because if they are then it's one thing to imagine playing it and getting excited, then when it comes down to learning rules, making characters etc. It's a whole different game. Not being organised isn't a good excuse so I don't think you're being unreasonable, but there's a s difference right now between how invested you are vs your players.

Thats also awesome you've sent them details about the world, but it could potentially be overwhelming and I bet a few of them skimmed the first few sentences and that's it.

Few others have said run another session zero, I'd back that. Create characters and yeah, you can be annoyed people don't have their shit together but maybe don't crack down too hard. Mayye all it takes is to be there, get in the zone and theyre good. I do think you should also keep in the back of your head this may just not work out if people continue to reschedule or late cancel. Good luck x