But they own about half (Disney Studios, Marvel, Lucasfilm, Pixar, 20th Century Fox, Searchlight, NatGeo, and I am sure I forgot a dozen others), and they might never licence it to a "competitor" again unless they are forced to do under some sort of FRAND unbundling of content and distribution.
And Disney doesn't own all the content. Netflix need only be the streaming provider other content makers choose.