wingsandsword
Legend
Fantasy, at least in gaming, is largely standardized through the influence of D&D. We've got pretty standard assumptions about what magic is, what it can do, about what monsters are out there, about society and generally how the world works.
Even if it's a "generic" adventure, the assumptions and legacy of D&D will be stamped firmly on it.
With sci-fi, there's no such single standardization of anything.
Basic assumptions about how the game world works don't hold, and plots that would be next to impossible in challenge in one could be trivially easy in another. For example, Star Trek type transporters and replicators could break a lot of plotlines. . .and Star Wars ships being able to cross the galaxy in a few days at most could break others.
Let's compare some of those assumptions, using some popular "franchises" as examples, since you mentioned Star Wars and Star Trek:
FTL travel. It could be like Star Trek's warp drive, where ships go FTL at a speed where they can get to nearby stars in days (or hours at best), and it takes decades to cross the galaxy. It could be like Star Wars's hyperdrive, where ships generally take only a few minutes or hours to travel from star to star, and crossing the galaxy takes a few days at most. It could be like Babylon 5 (or WH40k), where hyperspace is an alternate dimension with mysterious alien threats lurking in it that's treacherous to travel and requires great caution.
Psychics. It could be like Star Trek, where it's a natural thing that some non-human species have, but it tends to not be very powerful (at least for any species that regularly interacts with the rest of the universe). It could be like the Force in Star Wars, where the talent for it is very rare and warring factions of psychics, with a religious aspect to their beliefs and practices, are a major factor in the setting. It could be like Babylon 5 where they are licensed and registered by the government. It could be like WH40k, where it's licensed and registered by the government, but it also has some strong religious aspects that drive society.
Government. The prevailing government could be a totalitarian Empire with shades of theocracy (like WH40K and the Imperial-era in Star Wars), or it could be a peaceful, democratic society (like Star Trek or Republic-eras in Star Wars), or a contentious, warmongering democracy with shades of oppression and (like the Earth Alliance in Babylon 5)
Economics. You could have a post-singularity economy where money plays no part, or only a very small part of society, like most of Star Trek. You could have a very capitalist economy full of megacorporations and organized crime, like Star Wars.
Transhumanism. You could have a setting that has a strict limits or bans on transhumanism, like Star Trek. You could have one where cyborgs are relatively common, if only subject to a slight societal prejudice (like Star Wars). You could have a setting where cyborgs exist, but are rare and almost unheard of, like Babylon 5. Or you could have a setting where transhuman soldiers are a basic tenet of the setting, like WH40k
Try making adventures that can accommodate those various options and you'll find it's very, very hard to do so, especially to make more than just a few of them.
Even if it's a "generic" adventure, the assumptions and legacy of D&D will be stamped firmly on it.
With sci-fi, there's no such single standardization of anything.
Basic assumptions about how the game world works don't hold, and plots that would be next to impossible in challenge in one could be trivially easy in another. For example, Star Trek type transporters and replicators could break a lot of plotlines. . .and Star Wars ships being able to cross the galaxy in a few days at most could break others.
Let's compare some of those assumptions, using some popular "franchises" as examples, since you mentioned Star Wars and Star Trek:
FTL travel. It could be like Star Trek's warp drive, where ships go FTL at a speed where they can get to nearby stars in days (or hours at best), and it takes decades to cross the galaxy. It could be like Star Wars's hyperdrive, where ships generally take only a few minutes or hours to travel from star to star, and crossing the galaxy takes a few days at most. It could be like Babylon 5 (or WH40k), where hyperspace is an alternate dimension with mysterious alien threats lurking in it that's treacherous to travel and requires great caution.
Psychics. It could be like Star Trek, where it's a natural thing that some non-human species have, but it tends to not be very powerful (at least for any species that regularly interacts with the rest of the universe). It could be like the Force in Star Wars, where the talent for it is very rare and warring factions of psychics, with a religious aspect to their beliefs and practices, are a major factor in the setting. It could be like Babylon 5 where they are licensed and registered by the government. It could be like WH40k, where it's licensed and registered by the government, but it also has some strong religious aspects that drive society.
Government. The prevailing government could be a totalitarian Empire with shades of theocracy (like WH40K and the Imperial-era in Star Wars), or it could be a peaceful, democratic society (like Star Trek or Republic-eras in Star Wars), or a contentious, warmongering democracy with shades of oppression and (like the Earth Alliance in Babylon 5)
Economics. You could have a post-singularity economy where money plays no part, or only a very small part of society, like most of Star Trek. You could have a very capitalist economy full of megacorporations and organized crime, like Star Wars.
Transhumanism. You could have a setting that has a strict limits or bans on transhumanism, like Star Trek. You could have one where cyborgs are relatively common, if only subject to a slight societal prejudice (like Star Wars). You could have a setting where cyborgs exist, but are rare and almost unheard of, like Babylon 5. Or you could have a setting where transhuman soldiers are a basic tenet of the setting, like WH40k
Try making adventures that can accommodate those various options and you'll find it's very, very hard to do so, especially to make more than just a few of them.