As someone who does not share this preference/fetish, could someone who does like it try to explain the appeal?
I don't really get off on it but don't hate most forms either. To me "gender transformation" still is far too broad a category to allow for one all-encompassing explanation:
- Usually in a standalone "gender bender" doujin it's basically an excuse plot to have an incessantly horny female-bodied protagonist in an otherwise traditionally prude Japanese setting. Sometimes also because said setting does not otherwise allow for a female to have sexual agency in any way.
- Other M2F tends to emphasise "emasculation" or similar humiliation. Looking back at the previous point this usually involves dumping a psychological male into Rape Town as the female victim. Very similar to sissification, small penis humiliation, adult-on-shota femdom and the like in terms of style and presentation.
- I don't see much all-out F2M. "Partial" transformations are a complete mess, sometimes even growing testicles in addition to an arm-sized cock doesn't diminish her status as a "woman". Other times a 2cm clit is enough to make her doubt her self image. A fairly universal point seems to be a massive increase in libido, everything else aside that's a convenient excuse to just have lots of futa-on-anyone sex.
- At-will protagonist shapeshifting and forcibly transforming NPCs tend to ignore the implications and mainly serve as an excuse to have greater variety or simply more sex scenes without investing in additional non-sexual content (character development? who needs that?)
- Rule63 (genderbent popular characters) rarely seems to go very far or very deep, I reckon this mostly is an attempt to sexualise anything and everything to a hetero male audience. After all we also get "-tan" character porn and females with completely different body types frequently drawn as overinflated hourglass bimbos (or sometimes chibi lolis).
Basically if you discard all of those very few titles remain in my experience. Few enough to believe they cater to RL transsexuals and people who are genuinely curious about exploring different sexes (or gender roles) in a sexual context. Plus if they don't go
too deep philosophically most of them can probably work as a one-off "wake up with a penis"/"wake up with bobs&vegene" fantasy which seems to be common enough even in non-sexual contexts (basically "grass is greener").
What are other people's preferences/fetishes that might come off as weird?
Pubic and armpit hair, female muscle as long as it's below grotesque Hulk levels, slime/ooze inside and outside, any stomach distension other than mammalian-style pregnancy, female-on-invertebrate-monster (tentacles and other fantasy creatures also count), fantasy/alien female creatures...
And, contrary to what this context might suggest, I do not have a particular fetish for necromancy