An in-universe answer is that society is "transfobic" or at least not trans welcoming, since the trans characters hide this fact, although these characters are written by a guest author so maybe, like for race, only some place don't like some kind of people.
An out-of-universe answer is that you'd need to change too much stuff. For example, while in some cases you have phrases like "Dulrig said:<<You are a good [if Male "boy"/ if Female "girl"], [if Male "lad"/ if Female "gal"]>>" that can be easily changed, sometimes you have scenes that change based if you are male or female, like "Then Logan started to [if Male "stroke your cock saying:<<You're a horny boy"/if Female "touch your clit saying:<<You're a horny girl>>"]".
The thing that I don't understand is that I assumed that a trans guy would play as male and a trans girl as female having the opposite problem of yours (correct pronouns and incorrect body parts)