@xyzzy
I don't honestly agree with that. Some folk might write that for that reason, but it would be kind of pigeonholing an entire genre of stories into your singular view on it, which would be weird. I say this as someone that has written such a story myself.
This is perfect transformation into a female. Body and all. This is nothing like our current trans have to endure.
Our current tech only allows for very superficial alteration, with further tinkering being super invasive tampering of sex organs so they *look* like the other sex organ and that transition is irreversible.
Once our tech reaches the level where we can modify bodies and our brain structure perfectly without the person losing their sense of self (likely the brain shift would be gradual shift using nanotechnology/other methods so as to not cause undue feeling of alienation for the person).
Once we have reached that tech?
Then there will not be any trans, just perfect alteration into the other gender. Trans is imperfect as of now, which is a shame everything considered.
Now let's take me for an example. I am weird. I don't like yuri, I don't like yaoi. Sure, I can read both kind of stories easily, but then I do it for the story and fluffy moments, not for the romance or the less PG stuff. Trust me, I have experimented enough to know where I stand there. Be it irl or 2d.
But I am fine with genderbend (when it is perfect change of sex) stuff where a girl turns into a guy and dates a girl and a guy turns into a girl and dates a guy. That is in my personal segment of "straight". Likely because perfect transition will start to affect your brain patterns, your biology will start giving you different inclinations from before and so on. In short, the person may have "been" the other sex but they aren't anymore. At the very least, not in my eyes. Soul transfer into the body of the opposite sex is the same.
This only applies to stories where it is a complete physical change/reincarnation/etc and so on. If it is incomplete, herm or something along those lines I don't feel anything.
I am the type that goes, "if a person is completely physically turned into a female they are a female, if they turned completely into a male they are male." I don't judge the mind as either male or female (your brain can lean either way, but considering the variations, that is still not a perfect tell).
My long winded point? Don't pigeonhole us writers into one corner of your picking because you have a certain opinion on things. There are more than one reason to write these kind of stories other than what you pointed out.