This is untrue, female Morgan has a prior romantic relationship with the Russian engineer woman (I dont remember her name off the top of my head), same as male Morgan. So male Morgan is straight, and female Morgan is presumed to be lesbian or at least bisexual.Chloe was the main character of Uncharted: The Lost Legacy. I can't remember if there's any reference to Morgan's sexuality if you rolled female in Prey Granted, neither of these have romance options....
However, I don't think the games need romances just because
I'm sure this was done to save time, that way they didn't have to significantly change dialogs and data logs found in the environment...but in plays into the same trope OP is talking about.