I really hope what I'm about to say isn't offensive to anyone. I'm not stating facts, it's merely my speculation in conjunction with what's been my experience (based on observation).
I think it might be easier for men to wrap their heads around the fact that you're a woman, just because you're not like them. It might be a little harder for women, however, to relate and perceive you as being just like them, since your past life was still very different from theirs. It might be easier to say "you're different than me, so you're the opposite gender", than to say "you and I are completely alike, so you're my gender" when they perceive there to be some kind of difference.
I'd think this extends to males being accepting of FtMs too... perhaps women can accept FtMs better than men can.
I wound up on a lesbian forum by accident once and there was a thread about transwomen. The amount of bigotry, hate and toxicity just floored me. A few people were supportive, but most comments (and this is from LGBT women, mind you), were simply stuff along the lines of "I don't care if she's pretty, she'll never be a real woman to me"...
I think that no matter how good you look, some people are just prone to have a cynical side that makes them think your identity's not genuine. Some lesbians also seem to carry some sort of hatred towards men, so it's not too hard for me to imagine why misconceptions about transwomen appear.
I'm hoping that I've made sense, and I'm also hoping that your experiences don't get you discouraged. With these dating websites people can be backing off for multiple reasons... they might've been talking to someone else at the same time and opted to pursue them, they might be getting skeptical about dating and meeting people online, etc.
I think dating apps/sites are a little like meat-markets... there's too many people there, a lot of options, with no emotional attachment to any of them... so, if something doesn't go the way you wanted it to, don't assume it's because of who you are or something you did; there's a lot of factors that could influence someone's behaviour...