And how do you know whether or not that’s reflective of the world they live in? This is Thedas, not an alternate history to our own world. For all you (and, for that matter, I, as I’m not a writer) know, the majority of Thedas is somewhere on the sexuality spectrum other than ‘straight’. Maybe pure heterosexuality is looked upon as a quaint novelty.
Regardless, though, here’s the thing. There are lots and lots of games out there for people who are heterosexual. Most media and entertainment is built for them. Of course you’re not interested in inclusivity to a large degree - you aren’t part of the group that’s being ill-served by most entertainment. And it’s fine to say ‘I want my party to reflect the world they live in’, but at the same time - they won’t, regardless. Your party is filled with exceptional people, and the world is, by and large, not. Most dwarves aren’t like Varric. Most elves aren’t like Merril. Fenris is certainly rather unique within Kirkwall, and how many female pirate captains did you see walking around? Hell, there’s only one captain of the guard, and she’s adventuring with you.
If your companions are already exceptional in every way other than sexuality, why does it matter so much if their sexuality isn’t ‘standard’? And that’s assuming that Thedas isn’t a world where everyone doesn’t occupy a place on the sliding scale of sexuality other than ‘heterosexual’.