Maybe it never triggered in my games because I romance Astarion.
Aye, Astarion will be Lae'zel's first choice (in my experience) if you choose anyone else than her or Astarion. And unlike with Wyll, it actually happens (Wyll just talks with her). However, this can easily be excused by Astarion taking the opportunity to do the same with Lae'zel as he would with Tav. She is after all a very strong warrior and a perfectly fine option to try seduce for protection if Tav isn't interested.
I kind of view Astarion as being similar to myself, just flipped; he likely only feels both physical and emotional attraction to men, but over the 200 years he was having to bring people back to Cazador and essentially sell his body out to do so, he can likely at least manage an emotional attraction to a woman, even if it may not fully extend to physical attraction. I think if you put a male and female Tav with him, and they both tried to romance him, he would be more partial to a male Tav over a female Tav. That doesn't mean he can't feel anything for a female Tav at all... just, that preferences would still create a bias.
And this more or less highlights the issue I can support. All companions are written to treat the player character the exact same no matter the choices you make in character selection (with the exception of class, and sometimes race, mainly Githyanki I think). The only thing that will matter otherwise is your in-game choices. So the dialogue remains the same no matter who you romance him as. That's also how the game is advertised and as far as I know it works just fine for all other companions (if you can accept the Gale/Mystra situation).
Therefore, if a male Tav roleplayer will get the feeling that Astarion is interested in them emotionally and physically, but a female Tav roleplayer only gets the feeling that he's interested in them emotionally, then I can fully understand people have an issue with that.
basically, I always play myself in every game (lack of imagination, I guess).
Or you just imagine yourself being a lot of different things. Nothing wrong with that.
