Because if I were the developer or poster they might add to a completed game, or more likely a player could make a mod that many players would enjoy and encourage a replay. If you noticed those that had a similar request, I posted an encouragement.
Devs don't come here so no worries there.
As for mods, kinda impossible when it comes to anything to do with altering characters.
There are only a couple of scenes with Zent as a woman and no other artwork. That and modding RPGM games isn't the easiest. When it comes to unlocking things and modifying saves, easy enough, modding characters and artwork not so much.
In order to make Zent a full time woman someone would need to do all the artwork for that and this isn't DAZ or AI so they would either need to be an artist or commission one and that aint cheap.
Then they would have to code all that in on top of a game that is already a jumbled buggy mess. Then they would have to write all the scenes for the female version which means every single scene that character is in from the moment the change happens to the end of the game.
Modding in something like that in Ren'py using DAZ or Honey Select or whatever art engine they use would be a daunting task but doing that with RPGM and actual art work, you're asking for something that would be a huge amount of time, effort and money.
Why do you think no one had bothered with that in all the years this game has been around?
Not a dig at you personally but this isn't the first time i've seen someone mention adding character content to a game and I don't think some people realise just how much work that would be. Unlike an incest or gallery unlock mod, it isn't just a case of writing a bit of script. You are looking at many hours of work and, with art like this, at least a few thousand to pay for it with no hope of getting that money back.
It's a massive time and money sink that, even if it would be possible, no one is willing to do.