Christianity is the only forum that gets all that much activity, probably because Christians are a majority, at least in this country. As for other belief systems, they're on "minority" boards because the people who follow those faiths are in the minority. So isn't it logical that those boards get less traffic?
If people want to discuss religion and spirituality, they know to go to the spirituality forums. If you want to start a discussion on a particular religious topic, then by all means feel free. But bear in mind that a lot of LGBT people, perhaps trans people in particular, are likely to feel jaded about religion. Perhaps this is why there isn't as much activity in the religion forums as you would like. Apart from providing a space for minority believers to speak--which Susan already does--I don't see that she is obligated to do more, any more than she is obligated to promote, say, particular minority political parties or sexual orientations or anything else for that matter.
So I guess I'm with Finewine. I'm not sure what you're looking for. You are free to explore all sorts of topics on all sorts of forums, but that's up to you, of course.
Speaking as a person with a minority sexual orientation, a minority political belief, and a minority religious belief, I don't feel at all excluded here with respect to any of these areas. Do you? If so, why? I must confess that I'm kinda curious.