Because they assume that all romantic relationships only ever involve sex and that sex is the only reason you'd ever want to spend time with another person.
I can't understand why half the people clamouring for Story updates don't see romance options as Story. Or is it because it's no the "right" kind of story? What's also cute to see is people whinging over the SGR [Flirt] options in Makeb as being a waste of resources, but not the inevitable OGR [Flirt]s - maybe OGR [Flirt]s just spring out the ground, fully formed, like dwarves.
sadly I'm afraid we all know the answer to that one. :/