Because the reason Jin was notorious for having no content was because I never had interest in the character as it was. I'm starting to sound like a broken record now, and would really appreciate if we could move on from this, but I don't find bimbos attractive and have no motivation to develop a horrible sister who thinks about nothing other than being the best slut. That doesn't align with the theme of HH, much less than even the slave routes.
There also seems to be this idea that this came out of the blue, bit in Jin's first event, which has been there for years, she mentions the drugs, and that's when everyone finds out.
You're also asking me to double the amount of content I create for Jin. I have enough on my plate as it is. This is like asking for a whole new side character for Lin.
You also do have the option not to go through with it. It's a $1,000 option. I had player choice in mind. But this is a linear story, the same things even happen in the love and slave routes, to a certain degree. (example: Peni)