Ha ha, what do you know about the sexuality of Desmond or Steve? I know nothing about it, and considering their behavior and ideas there has to be something very entangled on that area.
I think people don’t speak of cis culture for the same reason there is no white history month.
You are right about pigeonholing. For those articulating phrases like the one I mentioned or similar ones the concept of “culture” is not important. You can swap that out. The point is delimiting yourself from those you tolerate.
Also outside the US, Western EU and other “1st world” countries, things are way different as the media portrays an almost universal homophobic perspective.