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.
Sex is not the hinge of my desire for same sex romances in the game. I won't go on a tangent, but let me just point out that sex is a part of life, and that in the end almost all romantic relationships (aside from those involving asexuals, I mean) will involve sex at some point to one degree or another. (And I totally support the idea of asexual romantic representation in games!)
For me - Jan'neria isn't celibate. At this point I just have to assume her flings all happen off camera, and that she's good enough at hiding them that no one ever catches on.
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.
Without going onto another huge tangent about realism, the Star Wars Universe, and Earth Human attitudes towards sex - there is some immaturity to this (former in your quote) attitude, which is caught up in all our baggage to do with sex. It also has to do with the fact that a lot of people seem to think that Star Wars is aimed at kids, and that romance of any kind should be kept away from them until they're 21 and/or married.
Here's another possible tangent - attitudes towards romance in non-romance genre fiction.
To be fair, I have seen a few detractors also saying they wished that BioWare would just leave romances alone, and not add to them, since they're all a waste of time and resources. But yes, it almost always seems to be aimed at SGRs without OGRs getting a mention. Next time someone comes into the thread with this "SGR is a waste" attitude, I might just point blank ask them about OGRs, and why it's not a waste as well. (I can predict their answer too - it will be "because only a minotiry want SGRs."
And if this is overly rambling or makes no sense, I apologise. I didn't get to sleep until 6am this morning, and was up by 10am . I hate nights like that.