These days Steam allows hiding games from your public profile by marking them as "private", meaning that people can't see that you own the game and can't see that you are playing the game (which is presumably what you would want if you were a fan of "Sex Adventures - Incest Family - Episode 9"). I imagine this is good enough for people so that they won't bother having a separate Steam account just for porn games, as having a single account is more convenient. There's a reason why people hate having multiple game launchers on PC.

https://help.steampowered.com/en/faqs/view/1150-C06F-4D62-49...