White Wolf came pretty close in the early 90s. Nothing last forever.
Seemed more like the second half of the 90s, especially when TSR started to go under, but yeah, WWGS was arguably a headspace leader in the industry there, for a while, even if it never 'won' in a $$$ sense, and didn't break into the mainstream. I wonder whether it'll be D&D (and thus fantasy's) dominance that "won't last forever" - or whether TTRPGs that'll fade away, without anything else ever successfully challenging that dominance, though.
I suspect a different culprit for why fantasy is such a dominant factor in TTRPG: The ability to participate equally.
I can only speak of my own experience, but when it comes to sci-fi, the science part of the genre can play a pretty big role in the game. And not every player has the same scientific knowledge and background.
'Hard' sci-fi can certainly get that way, sure. Not so much in, say, Star Wars.
But that brings up another issue: science-fiction is a more diverse genre than fantasy. Most fantasy, falls, in descending order of prevalence, into High Fantasy, Swords & Sorcerery (or, in contrast 'low' fantasy), fairy tales (and the folklore/myth/legends from which they were taken and bowdlerized), and arguably, magical realism. Science fiction, OTOH, has widely divergent sub-genres, Space Opera and Planetary Romance roughly correspond to High and 'low' Fantasy, Hard science-fiction is a major sub-genre contrasting with those two, then there apocalyptic, utopian, dystopian, and cautionary sci-fi. Science fiction can entirely appropriate the trappings of fantasy, too - Darkover and the Dying Earth are two long-standing examples.
What's more, for whatever reason, FRPGs rarely seem to be held to tightly to the conventions of the genre, and typically present a muddled High-Fantasy/S&S impression, with monsters & magic taken from myth/legend, as well. Fantasy doesn't cover as much ground, so an FRPG can prettymuch /be/ an FRPG, and represent the genre.
A science-fiction RPG, OTOH, has to pick a sub-genre, if not licence a specific property.
When I was playing sci-fi for the first time (after playing about a decade or more of fantasy games), I quickly realized how difficult it was to let go of the logic of science, even in such a "magical" setting like Rifts. ...
Nothing like this ever happened in any fantasy game I played. We were all accepting that magic > physics without a question. We didn't need realism.
I envy you the latter experience.
By the way, does anyone have statistics on the distribution of SF to F when it comes to literature? Is it even?
Sci-fi is way ahead, though not as much as it used to be in decades past, when fantasy carried an outright stigma. They're usually lumped together, today, and fantasy has been slowly on the rise for a long time.
You could view RPGs as avante-garde, that way, I suppose.
