The rationale why fantasy RPGs, and Fantasy as a style, are extra common than Sci-Fi, is due to the low expertise/excessive magic tropes. If your whole issues will be solved with wanting up the reply on a smartphone, properly, there’s simply decrease stakes than if a personality has to have a sword combat, and climb the tower, and rescue the truthful princess and recite the traditional incantation to seal the evil.
Clearly you possibly can have universe ending stakes in Sci-Fi, however that requires summary reasoning, and a capability to RP in a means that’s progressive as an alternative of regressive. Couple that with Sci-Fi video games and media typically being sooner paced, and you have a style that pulls a really particular demographic of avid gamers.