I think there are two main reasons it happens. One is because the characters that we are unable to have sex with fill a certain niche fetish, like Alma being a timid teacher or that girl you play poker with being muscular. The other one is the "forbidden fruit effect": if you can't have something, you want it more. A very common trait in human
Vortex00 said
Yeah the few cases are fine. Those are not really my issue. in UMCH I even added where maiko can try to have sex with savori dad.
My issue is where people only want a sex scene for a character mainly because they don't have a sex scene. Or at least that is how it seems to me after a brief discussion with that person. Yeah probably from conditioning, or actually makes sense in other game settings they have played.
I don't think conditioning has that big of an effect. While certainly for some it might be the case, personally whenever I found myself wanting an extra sex scene it was due to it filling a certain fetish of mine. I guess variety is key. Most people have a lot of fetishes and when you multiply that by the big audience that you have, the result is that the minority that gets disregarded feels like they want their fetish fulfilled.
To add to that point, people over-exaggerate the effects of conditioning. I think there are other underlying reasons that are not being considered. I have a bit of a background in psychology, so I do have a fairly solid idea about it.