[MixMasterLar]

I think it's down to the fact that for most people gender is defined by genitalia; so if you're claiming one gender but you clearly have the parts for another people are going to not know what's happening because you're challenging their definition of the word. Even people who are pretty ok with how one lives their lives are going to do a double-take because we're ingrained to automatically deduce as much info as we can as soon as we can do it; when something that -up until maybe a decade or so - was very reliable way to figure out gender proves to not be what the person identifies with it kind of throws folks off balance.

None of this is a problem in acting because in 99% of the cases the character is not trans and people can correctly deduce the gender by body type, with some notable exceptions I guess