I am assuming the vast majority of gamers is neither intersted in same gender romances, nor has a problem with their existance... Of course I have no hard evidence for this.
No, I mean, the people who want these romances wouldn't necessarily be happy with that.
Just off the top of my head:
1) "New characters" means we'd probably have to wait for an expansion...which could be years.
2) "New characters" also means you'd have to wait for lvl 50....or lvl 55 or whatever the cap would be when this expansion comes out.
3) Having the new characters shared amongst all classes is something I've seen people in this thread frown at. I believe it's seen as unfair considering each class has it's own OGRA for both genders currently (and some have multiple options).
4) When you limit the characters to 'gay, straight only' there will be players unhappy that they can't romance character X with their toon b/c of arbitrary gender restrictions...this would include people who do OGRA if they would ever make gay-only characters.