There is no political deviancy in it. It's not some slight-of-hand chicanery , its' a bit of PC and a lot of history.
In the beginning, there was a gay movement. The birth of that movement really occured at two places, Stonewall in NYC and Comptons in SF that were really what we would call 'trans' places now, but then - of course - there was no such language. Hell. They didn't really even have 'gay' yet. But those first events known as gay liberation
Lesbian came in the 80s, and as correctly observed it was done in the LG as a very deliberate effort to avoid misogyny. That LG and not GL was in every formal naming using that nomenclature. Though 'gay and lesbian...' is still the overwhelming choice of spoken American English usage. So that the LG (and not GL) was kinda of a victory of style perhaps, but no one else used it. B was kind of added as an afterthought, and they really, really don't matter.
So in the 90s efforts to include (after a lengthy debate BTW) T and I were made. At the time I argued that their issues/cause/demands/whatever, were different and SHOULD NOT BE included, and were dropped. The T activists - most of whom had been a part of the gay scene, or organized around the gay power structure, or just using common facilities - and having a lot more in common then they had different, including enemies - worked hard to put the T in there for a bunch of reasons. Later stuff Q/QQetc. were added in sequence according to the latest self-labeling fad in a historical progression.