I wish I had an answer, but I honestly don't know. I think it's mostly apathy for sure.
For me, I want to be allies to the LGBTQ community, but I don't feel it's my place to speak for them. As a black man, I often feel like my voice as an ally doesn't have the same effect as a straight white male ally, or a trans ally of course.
I get outraged and appalled at the injustices I see perpetrated against trans people and the LGBT community, but I admit I feel ignorant on how to express it in the same way I'm able to express my outrage about the topics that hit close to home for me. I have family and friends that are a part of the LGBTQ community, and I stand with them, I just don't feel confident in speaking with authority about what they face. I want to be a better ally, and I'm not sure how. And that goes for all of the groups I try to be an ally to (other marginalized groups like women, immigrants, Muslims, the LGBTQ community, etc etc). In my eyes, these communities are in much the same boat, and I feel like our successes can boost one another, but again, I don't know how to be an effective, supportive ally beyond speaking out when I can, donating to organizations when I can, and being an attentive and empathetic ear when I can.
Great OP, by the way.