Because it isn't who we are. If someone called be a lesbian, I'd correct them as well, even though I see nothing wrong with being a lesbian. In fact, if I were I would be quite militant about it.
I think that most of the GGs here are invested in supporting the community, since it is a way to support their partners indirectly. And when there are scads of CDers who minimize their motives by insisting on believing that what they do is just about the clothes (which is implied when they say that women CD when they wear pants), it perpetuates a sort of denial about their reasons for dressing. If that makes sense. And I don't know about you, but it disturbs me to see people in denial who perpetuate a falsehood, especially in forums where there are many newbies (in addition to their GG SOs), who come here looking for guidance or answers. And that's not even mentioning the huge numbers of people who do read this forum and who are not registered as members.
If scads of GGs should come to this forum and keep insisting that all CDers are gay, despite persistent explanations to the contrary, it wouldn't come off very well here and there would be just as much impatience among the CDers every time they read such a comment.
You know what bugs me the most? The CDers who come to threads like these and don't even bother reading the posts from the GGs and consider what is said, and who continue to perpetuate the nonsense.lol