It's funny. But these threads always focs on the importance of clear and explicit communication.
I'm somewhat bemused, because really anyone who posts on internet forums should know how badly explicit communication can fail.
The message you give is not the same as the one received. Twenty years of teaching have taught me explicit communication is only a very small part of what you need to do to set expectations.
If you say "no elves in this campaign" that may be interpreted as "No elves unless I have a really cool concept", or "No elves in the fiction but I can reskin the race as something else", because that is what happened in the past when GMs said similar things. If you say "low fantasy and low magic," that will likely be ignored because it's really not particularly clear and doesn't communicate any real expectations to the players about what they will do. If you say "this is a sandbox game, it's up to you be proactive and drive events - there will be no overarching plot", the players may not see how this is different to other games in the past where the GM has given them a clear direct plot but emphasised that they can always choose not to follow it if they really wish.
A lot of the time we gesture at the thing we want, rather than say it explictly - even when we think we say it explicitly. If you want to run a "highly political urban game involving the machinations of a small city state" you might be imagining bards and rogues and lots of characters with local ties - maybe a Fighter or wizard with an aristocratic background - but from the players perspective you haven't actually told them what you need them to do, so you get Druids and Barbarians and Dwarves from the mountains.
Session 0 can help of course - but that has it's own problems and can be too late if players come already thinking they know what they want to do and feel suddenly deflated.
Edit: Nothing communicates gaming better than gaming. If you have some unusual setting idea often the simplest thing is to make some pregens and run a oneshot. By the end of the session players know what you're trying to do, and they know if it actually interests them. You can then let them make characters and start the game proper (and it's surprising how often players ask to continue with the pre-gens).