Early fantasy and science fiction took place in times the authors lived in. Why did fantasy become overwhelmingly medieval and science fiction become overwhelmingly thousands of years into the future? Why didn't we get Great Depression fantasy, WWII fantasy, hippie counterculture fantasy, etc.? Why didn't urban fantasy become the most common form of fantasy?
>Great Depression fantasy
I mean, Grapes of Wrath had some elements that could be arguably considered "fantastic" in that sense. But holy hell I'd read the shit out of some Great Depression fantasy.
The only Great Depression fantasy I can think of is a TV show.
>all dystopian fantasy takes place in the future
>just everything is medieval as fuck
>battle axes and swords and magic
>a lot of fantasy is disguised as science fiction
>star wars is fucking wizards shooting lighting and fighting with swords because "the force"
science fiction is generally set in the future because it's easier to speculated on how scientific advancements might affect what it means to exist and what life might be like in the future.
>why didnt urban fantasy become the most common form of fantasy
because western civilization peaked 1500 years ago and everyone wants to be a roman.
It's been alluded to, in particular re Fantasy, but the two genres have a fundamentally different essence and purpose. I think escapism is a decent way to encapsulate Fantasy, but Science Fiction is oriented toward 'what if' and possibilities and how things might develop. It seems to me like that's what has driven the tendency mentioned in OP for Fantasy to be set in the past and SF the future.
I like it when authors pretend to be science fiction but invent a time machine that takes them so far forward in the future that they end up in the past.
I assumed fantasy was always only medieval because the people of those eras already believed in a lot of the kind of thing in most fantasy, whereas if you encountered a troll or Dragon in the wild west, you can only imagine them freaking out, while a medieval would be surprised, but it is already a thing they believe exists.
Also, we have Victorian fantasy: Dracula.
And Victorian SF, for that matter: Frankenstein.