Might be that the total subsumption of all issues to class means that LGBT people can feel more welcomed in tankie communities as individuals because tankie communities don't regard the issue as of importance. Rather than feeling the sting of rejection in right-wing communities (and there are a terrifying number of right-wing LGBT folk) or the strong emphasis on LGBT community and culture in many left-leaning communities that may leave some feeling 'out of the loop' and depersonalized, even if that's not the general feeling or the intent.
Alternatively, LGBT people are just people, and people are often dumb. Whichever.