Indeed. Disney would be foolish to lease out all their most popular works. Disney needs to hold on to every scrap of the Star Wars franchise that people still like.
That is an issue with Netflix as a whole. When you get down to it, their suppliers are their competitors. It's a testament to the business savvy of the Netflix team that they are even still in business now.
When streaming was in it's infancy Netflix was able to get away with this because media companies could lease out their old material (which they weren't making any money on anyway) and make some money. Now that more people are trying to compete directly with Netflix they are charging Netflix more for streaming rights or saying no outright.