I know the reason, and I will say it; loss of male privilege. The other reason is fear of the unknown, in other words what will we (I'm still wrestling with this myself) lose if we come out? I am out to my wife, my therapist and one old friend from high school. Another reason I'm not out is that my wife fears the same things I do, and fears losing respect "as a woman" for having married a man who wants to be a woman. I sincerely want to come further out in the future, but with a wife and children involved, it is not entirely my choice because it effects them as well as me. If I had accepted what I was before getting married... That is my great regret with regard to this.
All that said, you are absolutely right. It is like the Gay Rights movement, homosexuals didn't start getting respect until they stopped hiding. CD/TG/TS people won't gain respect until we stop hiding, which means pulling on our Big Girl panties and telling the world that we want to play or even be a girl.
Anna