You ask why can't these relationships be gay. I ask: Why can't they be straight? Most estimates (as difficult as it may be to gather them) put the U.S. LGBT population at or around 3.4% (
http://www.gallup.com/poll/158066/sp...tify-lgbt.aspx) while the number hovers around 1.5% in the U.K. (
http://www.bbc.co.uk/news/uk-11398629). Heterosexuality is the norm and/or average, so why should homosexual relationships be disproportionately represented in fictional media? Why have them in there just for the sake of having them in there?
And honestly, does it really matter who is fucking who in a story? The only reason to switch these relationships around is to make a political statement--they have no bearing on the content or depth of the story itself.
If you want to advance a political cause and/or an agenda, that's fine. But be honest about it.