I think I have figured out LGBT.
LGB is with regard to 'sexual orientation', while T is with regard to 'gender identification'.
LGB persons have a different sexual orientation from heterosexual persons, but LGB persons have the same gender identification as heterosexual persons.
T persons have a different gender identification from heterosexual persons, but T persons do not necessarily have a different sexual orientation from heterosexual persons.
While all T persons are gender non-essentialists, not all LGB persons are gender non-essentialists. This is one reason why LGB persons may not appreciate being associated with T persons. Some LGB persons think that T persons harm their cause.
Anyway, correct me if this is somehow inacurrate.