And, even then, that's not really an issue as well. Sure, you and the other players had a hand in building the world, but, good grief, it's a WORLD. There's an awful lot of white space still left over for exploration.You (the players) don't explore the world you built. Your characters do.
If it's important to the players to experience an unknown environment, then they won't want the level of agency that Hussar is advocating for.
The Forgotten Realms is well defined in source books and expansive fiction that a lot of players are familiar with. It's perfectly feasible that (some) players can still have exciting adventures in that setting, despite the familiarilty. Similarly, players (some of them) can have exciting and engaging adventures in a world that they help define either before or during play.