MARVEL does not suffer from this lack of material to create new movies from. All they have to decide is what movies *not* to create, because once someone says "Captain Marvel is greenlit", they all basically know what to do. In Star Wars, they have no idea. So they just rehash the same kinds of people, the same kinds of robots, the same kinds of biomes, aesthetics and so on.
Thing is, they can pull a lot from the Extended Universe, in the same way that Marvel is pulling from the comics. I mean, you could argue that most of the EU is kinda crap, but so is most of Marvel's comic history, and a lot of Marvel's success has not been about rehashing stuff most people already know, but looking at underappreciated or underdeveloped material and putting it in a new light (BLACK PANTHER). Disney already has plenty of creative talent that is willing to put out some interesting pitches in the new extended universe stuff: The comics, for instance.
Even then, none of this was present in Solo's marketing push.