If you look around, in general there are actually very few distant future (i.e. Star Trek, etc) or distant past (i.e. Star Wars, etc) Science Fiction based erotic and/or porn themed VN/Games in general... Let alone parody of Star Trek or Star Wars... And the few Sci-Fi ones out there, are not all that good in the first place... I've ran into a small few I've enjoyed, while I've run into lots that just aren't all that good and/or suck... You get more "slightly sci-fi" VN/Games on the market typically, that usually revolve around technology or chemistry based corruption/manipulation, based in a more modern setting, then others in the true sci-fi arena...
For long standing and highly evolved stories like Star Trek and Star Wars, you tend to have a more fanatical fan base... One that is highly protective... Does that influence the lack of Adult themed Parodies? Maybe... Or it could just be a lack of developers interested in using those platforms... I think it's most likely, just a general lack of interest in developers doing it... You don't see as many Parodies of anything really, compared to original works or generalized copy cats... And over half the Parodies I've tried, they were either not funny at all, a mainstay for a good Parody, or they were not entertaining due to poor writing/design... Sometimes a Parody VN/Game is only really funny to the developer and maybe a minor few, rather then the masses...
In any case, yes, it would be nice to see more Good Sci-Fi VN/Games, especially revolving around some of the bigger series like Star Trek and Star Wars, etc... But if the developers are not interested, or up to speed on the subjects, or any good at doing justice to those series, then you just will not see them being done...
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