The have been honest.
Simple truth is that flying world and the not-flying world are different. They have a different feel, offer a different experience, etc.
They gate flying so that the bulk of the player base experiences the world the way the designers want it to be experienced. Going up the roads, running in to other people, fighting through the trash, not riding through entire camps to aggro them and get clobbered. “Go around, take the bridge.”
That’s it. That’s why they gate it.