Don't forget Sigurd and Brynhild, Yu Mei-ren and Xiang Yu, and Orion and Artemis. Personally I've never seen people get upset about gacha characters being in relationships with other people, though most don't do that in the first place for obvious reasons.
Most people playing this game are straight(ish) dudes. Obviously if I could turn a character with sexual content into a girl, I'm gonna do that because I'm not into guys. People would rather interact with content they're actually interested in. Why do you act like this is some negative character trait?
You know not everybody gives a shit about lore, right? People can just enjoy the sex scene for what it is without quaking in there boots wondering if it perfectly aligns with their character. If they have a sex scene they're interested in and it doesn't completely fuck things up with other characters, people are usually gonna do it. Even regardless of that, have you ever thought that also might be why some people like it?
Yeah punish people for enjoying sex scenes in a smut game, I'm sure that'll work out just fine.