Frankly, at this point, Fox is trying to milk every penny out of the OT they can before they lose the rights to Empire and Jedi. If that means cooperating with Disney/Lucasfilm on a physical release, they will do that. In the end, it’s about money, and that is the only way they can make any more off those two movies. The current Blu-Ray master has been milked dry—two “Complete Sagas”, two OT boxes, and the steelbooks. They need a new product now—namely 4K and/or an OUT BD, both of which will require a new master—to make any more substantial money before their rights expire.
Star Wars? Now that’s interesting. Good point about Fox access to archives. Fox could probably unilaterally release Legacy, though, if Mike is cool with that and Disney is not willing to cooperate on a restoration.