The unwritten tg story rule - never change back the transformed - why?

Hi,

there's one thing I'm wondering about... I've been reading tg fiction for over ten years now, and during that time, I've come to realize that there seems to be some kind of unwritten tg rule: Never ever change the transformed person back into a man - at the end of the story, he, now *she*, will be stuck as a woman.

Really, in more than 90% (probably 95%) of all stories I've read, this happens - the transformed character stays a woman (sometimes because she likes her new life, but most of the times because of bad luck or other things).

Even when one is willingly trying out being a woman for a short time, with the intention of changing back after his experiences, (s)he somehow gets stuck anyway.

When I look at some popular story universes, I even notice that this "being stuck" is a detail apparently deliberately designed into these universes. For example:

Jennifer Adam's Altered Fates: Often, the medallion inexplicably vanishes or is given away and the main character, who mostly only wanted to change temporary, gets stuck as a woman
ElrodW's Bikini Beach: The life pass which often traps people in their new lives, although it happens quite more willingly in this universe
ElrodW's Morphic Adaptation Unit: The 4-day clause of course
Spell's R Us: The wizard who tricks his unsuspecting customers

On the other hand, story universes which don't offer a ready possibility of getting the main character stuck in her new don't seem to exist or are not popular. Cabinessence's Magic Depot comes to my mind. I always thought that this universe offers a lot of possibility for cool tg stories, but somehow, nobody seems to use it... ^^;

Since my preferences lie exactly in the "voluntary, temporary change without being stuck" category, I'd like to evaluate the reason for this... why is it so important for the main character to get stuck in her new form? Isn't this kind of cruel, a bad (in the sense of unhappy) ending...?

Are there more people like me who'd like to see voluntary, temporary changes without any catches at the end? :)