They are lumped together because society has done so already. They are outside of the norms and are sexual minorities that challenge the old assumptions and fra

They are lumped together because society has done so already. They are outside of the norms and are sexual minorities that challenge the old assumptions and frameworks like men always marry women and the only men without testicles are eunuchs. It is true that LGB are orienation while T is gender identity but they face the same issues. In a societal context where they were all essentially "equally normal as cis-straight" there wouldn't be much of an association just separate categories.