Part of the drive for guys is to propegate the species. Maybe he's a neanderthal, and maybe he's not. Maybe he's anti-something, and maybe he's not. Lost in the discussion so far (I'm only on page 4!) is that in this case, he knows up front that he can't continue his line - so why try (again)? Concious thought, instinctual feeling, or phobia laden jerk, it doesn't really matter - that part of "being a man" is lost. The strength of that drive has an impact, as much as does being a neanderthal.
That's about the only reason to "have to" disclose that you're a TS too. Your future hubby really doesn't want to hear it from the fertility clinic, any more than some of the guys on other parts of this forum don't want their wives to find the box in the back of the file cabinet.
In truth, isn't reproduction the only difference? Other than that, are you not physically, mentally, emotionally, and legally a woman? Couldn't "why" be put in the same bin as "how many others have you had before me?"