So, full disclosure, I am cis, and exclusively attracted to men, since that is sure to influence my viewpoint on this.
I am of course referring to this: https://tvtropes.org/pmwiki/pmwiki.php/Main/EveryoneIsBi
I think that this is essentially the laziest way to do gay/bi representation. Everyone's just inexplicably bisexual. I'm sure some people are happy with that for whatever of what I am sure is long list of valid reasons. If you like games where you don't have to worry about this, I'm not arguing that you shouldn't. And I can't know how bi people feel about this at all from my experiences alone, so any bi people with an opinion on this please do share so I can further develop my own perspective on this.
Like, when I want representation, I kind of want it to reflect the real gay experience. That means the tragic bits too, including that not everyone is on the table as a potential partner. And that doesn't even mean having only one in ten or so characters being an option, I have seen VNs where there are so many gay people that it is clear that there is something in the water making everyone gay, that represent that aspect better. Something like getting the wrong signals and getting turned down by someone who can't reciprocate your feelings towards them? It's a tragic experience, but one that can be worth representing in media, because it's a real experience. But I don't know if that ever will be represented properly, queer people are already a small portion of the market, queer people looking specifically to be tragically rejected by a straight person have to be an absolute minority.
Why I say this is possibly a step backwards, is that games like Dragon Age: Origins (2009) had romance options that all had distinct sexual orientations, you had two straight and two bisexual companions you could romance. Fallout NV had no real "romance" options with companions, but did have Veronica and Arcade as distinctly lesbian/gay. And honestly, this seemed a bit more... it feels really fucking wrong to say "natural" in this context, but I will say it feels uncanny in comparison when I can put on a necklace in Skyrim and suddenly everyone I have run an errand for wants to marry me. Or that every companion in Fallout 4 will constantly forcegreet me after I max out friendship trying to get me to start their romance line.
It also just feels so much like an afterthought in comparison as far as the character writing goes. Looking at the games I mentioned, the distinctly bi and gay characters do feel like they have bi/gay energy, and that feels like it adds to their character design. I don't feel the same representation I felt with someone like Arcade Gannon in this type of setup, where there was a character who was like me (though to be fair I didn't know I was like him at the time I played -- well, I kind of did, but I was in deep denial at the time -- it's complicated), it just seems empty -- none of these characters are like me in that way.
For video games specifically, I think this comes up most often as a way of conserving resources. Imagine a game where you have six companion characters, three men and three women, and you want to do gay representation, do you just make one of the men and one of the women gay? That feels really artificial and token-y. But adding more companion characters in order to get a more "natural" split of sexuality also isn't an option without making them all extremely shallow and unconvincing. So the devs come to a simple conclusion: give all romantic agency to the player, and make whoever they romance interested.
I would agree that that is also a bit uncanny and leaves the door open for a game that explores sexuality better, but adding scenes into a video game is expensive - Bioware has the scratch to give every companion character an explicit sexuality (in fact the only game of there's that does the "everyone is bi" trope is the notoriously cost-cut Dragon Age 2) but a mid-budget action game that wants to have romance sidequests has to make the most of what they got.
But then the next step is we ask why devs have limited resources, which is usually capitalism, which opens up a path to doing better; We get rid of the profit motive in making video games and maybe devs will have the space to have more fully realized, unique characters in their games.
Which, coincidentally, is how Skyrim solves this problem; Lots of modders have come up with romanceible (or just fuckable) NPCs to add more depth to the game's relationship systems because they can operate without the constraints of trying to make a profit.
I'm not trying to rag on you, I just feel it's important for us to say out loud that this is once again at least partially a case of false scarcity imposed by capital.
If only it were considered good practice to make your game 100% moddable. Especially with games made in popular engines, you would think it would be easy.