Yeah, but that won't happen. Imagine pissed hetero part of Astarion's fanclub if he was only gay. All those pretty drowish girls wasted.
Hedonistic Sybarite centuries old undead vampire doesn't seem like a bad fit for a pansexual
The reson some people might like Herosexual or Playersexual romances is that for people who generally don't see themselves represented in other games with regards to their sexuality, being able to flirt with and romance whoever you like, without facing rejection, can be freeing.
On the flipside, it's just not realistic. In real life, everyone has their preferences, sexualities and other reasons for being attracted to who they're attracted to. It's hard to get immersed in a world where everyone likes everyone, and has no preferences. But some people don't give a shit about realism in this regard, so it all comes down to preference, hah.
Honestly, in my opinion, playersexuality is just lazy with regards to representation. As a member of the LGBT community, I think that going "Oh you can just fuck anybody!" does not solve the issue of meaningful and well written LGBT characters in gaming. Instead of basically erasing all sexualities, why not make some straight characters, some gay ones, and some attracted to all genders. This is something Dragon Age did (in the first and third game, at least), and the romances in those games are extremely popular.
Also people are just going to create mods to get with whoever they want anyway, so in the end it doesn't even matter lol.
The first point leads to what I think must be a big divide between two types of players, people who play RPGs to self-insert, and people who are more interested in taking on a role unlike themselves, because I'm more interested in the later, I find myself more amenable having things taken out of my hands by the story, world, etc.
The second point has a lot to do with why I don't like when this happens in games, if your character is just a cipher to the NPC because they've been written to respond to you and the circumstances of the relationship without regards to any distinguishing attributes then it's very easy for me to see the seams in the writing, different input same output means the input becomes perfunctory, and the relationship is a little more meaningless because of it. If you want to write characters who are bi-sexual that's good but you have to at least address it for it to be at least a little bit believable, instead of what we usually get, people who avoid the topic because they've been written to cater to all of takers.
