It does have to do with transgender people because we don't fit into the gender binary, as much as we like to yell about how we're just as much of a woman as a GG (and vice versa for trans guys). This is where sex and gender both matter, because a trans girl who has not gotten her surgery is still a woman, but has the organs of a male sex. Sex is part of attraction, so a trans girl is not quite the same as a cis girl as far as the gender spectrum goes. Yes, we're women, but we're a different kind of woman.
There are guys (and girls) who will date cis women but not trans women (not that I had to tell you that). If we were exactly the same as far as sexual attraction goes, the trans part wouldn't be an issue--but it is. It sucks, but it is what it is.