It's don't believe that it's (just) nostalgia, I think it's something far more insidious, and I doubt that Disney is doing it consciously: Neoliberalism (or postmodernism or whatever) has robbed us of our cultural capacity to create the New. Like Fredric Jameson prophecized back in the 80s, late capitalisms culture is characterized by repetition and pastiche, with old forms and old content being recycled, the only new stuff we get is technology. Mark Fisher argued that the movie Children of Men is also about a society like ours, where the catastrophe that made almost everyone infertile is a metaphor for the inevitable end point of our own slow decline of collective imaginative and creative ability. That's why all those Marvel films suck so much ass - they're obviously competently made, the actors are good, the music is alright etc. - but at the bottom, they're really only rehashes of stories that came out as comics like fifty years ago, only the technology is now better so we get cgi animated Hulk instead of some dumbass in a green onesie jumping around a set made out of cardboard or something.