It still seems odd because it's basically just porn at that point, so unless someone exclusively watches POV porn it's pretty much the same.
Porn generally doesn't work nearly as hard to establish a connection with the characters, and also is very rarely as self insert as an AVN imo... it's very different. Also different mindset when approaching the media. I don't approach porn from a LI perspective at all, it's purely a voyeuristic thing.
Within the framework of most AVNs (and pretty much exclusively the ones I engage with) I am ostensibly the MC, and therefor I've no interest in seeing a LI engaged with someone else, even if they're not currently with MC. I don't think it's NTR or makes MC a cuck or anything stupid like that... I just don't have any desire to see a partner's past like that.
I'm married IRL and my wife was engaged before meeting me, I'm aware of that I've talked to her about her previous partners where relevant and don't have any jealousy towards those men, I still would be pretty upset (not at her, but just in general) if I stumbled upon videos or pictures of her with them from when they were together before I was even on the scene.
I do admittedly attach considerably more emotional significance to sex, and would never IRL have one night stands or flings or fwb or anything like that... I'm very much a sex = long term committed relationship type person (I realize not everyone is that way and I'm not making judgements of people who are more of a sex = enjoyable no strings activity types) due to that at a certain level of detail thinking about past romantic endeavors of a current LI/partner, gets me in my feels some kinda way, so I avoid that where possible.
For this reason while I have no issues with the LIs in this game having prior experience, or even going on dates/hookups etc before shacking up with the MC... I'd just rather not see it, and so I appreciate the existence of that option such as it is.
*end overly long explanation, caused by inability to not overly long explainate.