Because there are no distinction between sex and everything else.
Woman said hi to you -> you can fuck her right here and right now.
Roughly speaking, there are no 'friend' and 'lover' concepts. Everybody is a lovers instantly upon meeting, which is actually a leggit power fantasy (What, woman that dont say no? Its a slut. What? All womans dont say no? Fantasy, power fantasy). I know, 'Its a porn game', but without any feelings attached to the character all interactions with such character and character itself becomes dull.
Eh.
The thing is none of the writers within the team know how to write romance very well, likely because they themselves just haven't experienced it in a healthy manner or at all.
Romance in porn games just equals to pressing the talk button 5-6 times then smashing or doing a quest then smashing.
Personally I don't really find a meaningful distinction between friends and lovers if all I need to do to ungrey the fuck button is to press talk and skim over 2-3 different backstory drops I couldn't give less of a shit about. I wouldn't really call that attaching feelings to the character because people in real life aren't willing to actually go on 2 hour tangents of oversharing with you. Now the second measure porn game devs take with that is to split the "talking" phase into forced time limits, where you have to visit them every once in a while to progress. But again, all of this feels arbitrary as shit rather than an actual person to person interaction.
There's no real way to win when it comes to writing proper romance in a porn game, or at least I haven't really seen any.
I personally think romance in porn games can only really convincingly work by not trying to be like a "pure romance" at all, e.q. love born out of something other than traditional courting. Like Arona. I can somewhat buy Arona's romance because she is a batshit insane woman from a batshit warrior clan where defeating the shit out of her dozens of times might actually have gotten through her in a way. And you still have to take a while with her afterwards until she opens up. I can't buy any normal romances ever though, it will always devolve to shitty talk scenes.