Because that situation involves a naturally intersex individual. Trans people are not intersex. You are comparing apples to oranges.
I already made it clear earlier in the thread that initial attraction is andro/gynosexual in nature. There are many layers to attraction, however, and attraction can be lost for various reasons.
It stands to reason that someone 100% attracted to males would desire 100% of the same. Trans men are, technically, 100% female. There is no getting around that and for 100% gay men and straight women is an understandable deal breaker and does not mean they are de-legitimizing someone else's identity or being hateful.
Buck Angel actually did a video on this a couple of weeks ago regarding this specific topic, and honestly I feel as a trans man (as well as adult film performer) he has more authority to elaborate on this and does so very well.