Trying to understand this idea just hurts my brain. I thought the supposedly prototypical straight fantasy was a threesome, so therefore bi women = the ideal, and straight = bad. But maybe not? I don't know.
I've seen at least one straight woman who was a major Cullen fan say that if Cullen was romanceable by both men and women she would lose interest in him as the idea makes her uncomfortable, so it's a mentality that isn't exclusive to straight men.
But a companion can be both whereas an NPC can only be one.
The original point i objected to was those saying both straight genders should have the NPCs while others get 2 companion choices.
Companions are never treated as such, though. You can literally never take a companion out adventuring with you and the story won't acknowledge that. They'll act like they fight beside you all the same.
An NPC romance acknowledges that they're not fighting by your side, so it tells a different story.