I think this one was on its wheels. But presumably the key factor is that it was owned by NASA, which makes it I assume much easier for NASA to do...whatever with it.
Getting any of those planes outside of their museums would be logistically difficult, and of course it would immediately be noticed. And even if you can rent a hangar big enough, and secure it, then you're stuck at BFI/IAD/Wright-Patterson trying to do this impossible task.