Initially, at snonewall, and even until the 90's, many many TS started in gay circles because lets face it, there was not much options, much confusion and little information.
In support groups around 90, many could be called drag queen, by the way they dressed and coming from the gay scene. In current support groups, I don't see that anymore, only the older TS 30 and over remain, most of the "gay TS" transition by 18 often doing DIY. They tend to stay away from support groups which have older TS.
So, initially, the T was legitimately tagged to the LGB because it was mostly the same crowd, now it may needs to be reassessed. Keeping it there, but also finding out why it should be there.