Every single large server in this federation has at least one Star Trek community. There is even an entire server dedicated to Star Trek.
Not only that, these communities are some of the most active I've ever seen. There is no other franchise I know of that dominates the federation as much as Star Trek does.
So, what's the correlation with Lemmy and Star Trek? Why not other sci-fi series? Please, are there any connections?? Is this all coincidental?
So others have already talked about how great Star Trek is. I agree with them, but I think that literally everyone has missed the point of your question:
It's its own lemmy instance. It was spawned from the migration away from reddit, and it's stayed alive since. So combine an active former-reddit community with lemmy and a good reason to all rally around, and finally the final ingredient of federation, and the Star Trek related rooms will always be on every server, and they'll always be populated.
Yeah, I think this is a big part of it. The Star Trek sub's total abandonment of Reddit and conversion to a standalone Lemmy instance during the Blackout was a big deal and a big driver of traffic in those days and beyond.
Star Trek is big in the Threadiverse for the same reason that Earth is big in the Federation. They were a massive force in the early days.
Both this and all other answers are good for different reasons. From what I'm reading, the beliefs and politics displayed within Star Trek are beyond progressive for the time it came out, while also shaping sci-fi. This creates a very committed fan base that when Reddit started acting up, they were able to move a large chunk of their user base away to Lemmy, since Lemmy is filled with similar-minded people.