Why do owners of airplanes need approval to fly? It's not like the air is owned by anyone? Just because someone doesn't own something doesn't mean you can just

Why do owners of airplanes need approval to fly? It's not like the air is owned by anyone? Just because someone doesn't own something doesn't mean you can just launch stuff up there with no regard for other such things to be launched/already in the air. Things can and do collide, and the ramifications of that are actually much more dangerous when you don't have an atmosphere to pull the pieces down in the event of a collision.