Offhand thought - I wonder if part of why sci fi and fantasy are so huge now is that a lot of the genres that would've scratched the same escapist itch are now hard to do inoffensively. Like a lot of 19th century adventure literature is oriented around white adventurers visiting strange cultures, romancing hot locals, stealing stuff, and getting away. Setting it among aliens or elves or whatever allows the same story, theoretically minus the dehumanizing.