It is not done that way because that was the way it was done in the past but because that is what the hobby demands. A flight sim is NOT a stand alone game, it is a platform designed to be added to by those with the expertise to provide the quality add ons. Not only does that make it “okay”, it makes it required to fulfill the expectations of the flight sim community.
My question would be, why do I keep hearing people clamoring for a complete sim right out of the box. Who would bother creating new content?
I will never understand where this expectation comes from when MS/Asobo stated from day one that this was a ten year project.