why is it?

what when I tell people I'm transgendered they always compare it to being gay? Not offended or meaning to cause offence by wondering it here, it's just a curious occurance that has happened four times now. Is it because my being attracted to men that somehow people assume I'm somehow a gay man who dresses as a woman? That's not how I want to be seen or thought of, I'm a woman and want to be treated as such, after all a gay man wouldn't want to be thought of as a woman, would he?
Gender identity is unrelated to sexual orientation, many times they run along the commonplace binary system that society often believes is the be all and end all of life, which it isn't. My genetic sex is male but my gender identity is female, this has no bearing on wether I fancy men or other women. I'm just curious as to why so many people think they're linked, maybe it's how they're raised? I guess there's still a long way to go in educating people about themselves and who we all are as individuals.