Which SciFi ttrpg has the largest player base?

[warty goblin]

It's interesting to note that this situation is basically a mirror of fantasy and sci-fi as a whole, where Lord of the Rings is still basically the fantasy novel to the point that having elves and dwarves is basically considered the default. Meanwhile, there are some big sci-fi franchises (Star Wars¹, Star Trek, etc.) but none with the sheer influence on the genre that LotR has, I think.

(¹ Let's not get into the whole "Is Star Wars sci-fi or fantasy?" discussion right now)

I don't think this is true of fantasy anymore, outside of gaming. I can't think of the last time I've seen a fantasy novel with dwarves or elves in it that wasn't set in a universe created like 20+ years ago. Anymore one hardly gets any sapient species besides humans at all. Nowadays it's all oppressed wizards solving colonialism.

Within gaming related properties these remain much more default, probably because they require basically no explanation at a thematic level, and remain useful shorthands for particular gameplay archetypes. If you want to be tough, go dwarf. Fast, go elf, etc.