Probably has something to do with the fact that, since the vast majority of people are heterosexual... so are the vast majority of trans people. Meaning that they are exclusively opposite-sex attracted. Thus, most transwomen only pursue women, and most transmen only pursue men.

So why are they always going after GAY people, as opposed to, respectively, straight/bi women or straight/bi men? In a word: "validation". Trans people find even the possibility that someone could be attracted to them based on their real sex intolerable. So transwomen shun any woman who's male-attracted, and transmen shun any man who's female-attracted. Which is to say... anyone of the opposite sex who is actually capable of being attracted to them. Instead, they insist on those of the opposite sex who, by definition, AREN'T capable of being attracted to them: gay people. Thus, only lesbians and gay men will do.

Also, I'm 100% certain that all of the people saying "genital preferences" are wrong have a "preference" themselves.

Oh, no doubt: this is how human sexuality WORKS, after all! I mean, monosexuals (gay and straight people) really have what is more properly termed a "genital requirement": you'd better be of the one sex that they're attracted to, and have the primary sex characteristic (genitals) to match, or forget it. Only bisexuals could be said to have a "genital preference", and then only if they're more into one sex (either for the time being or permanently) than the other; even so, what attracts us to men is their maleness, and what attracts us to women is their femaleness... just like monosexuals. We just aren't wired to respond sexually to mismatched sexual characteristics. NO human being is, as far as I can tell. So transgenderists need to quit demanding that we act like some alien species they've invented for their bargain-bin-quality sci-fi novel.