I'd only say that LGB-and-T is this way because these groups of minorities were\are historically targeted by the same sort of bigotry, so they united, shared safe spaces and were supportive of each other. You may say it was dictated by real life more than theoretical arguments. Singling out one part of it for some reason would mean abandoning them and weakening the coalition. There's a negative probability that after trans people are excluded, other groups won't be challenged next. You know, not long ago being gay was treated like a mental ilness and there was a conversion therapy to bully them into becoming hetero. It may start to be a thing once again.