A few notes of context that may help here:
1) Japan historically does not understand the PC modding community. It is only tolerated when it goes through official routes. During Automata’s development, I was trying to bring in a famous PC modder to make the PC port bulletproof. When I left the company, unfortunately that advocacy went away, and that person was not able to be involved. I was pretty sad about that, but without strong advocates internally to bring that community into the tent, it is just simply not understood.
2) Japan is culturally STRONGLY aligned with “do not cause trouble for people.” Westerners view these mods as game preservation/extension; Japanese feel that you should not preserve or extend what does not belong to you because who will take responsibility if it causes issues. Who will take responsibility if someone mistakenly blames the original creators and not the modder for said issue. It is all about not creating issues for folks, or 迷惑行為 (meiwaku kōi) which can be translated all the way from annoying to legal standards like harassment or disorderly conduct.
3) Because of the above, Japan has always been strongly aligned with creator rights. You always try to get permission. Yes, there are pockets of work like Doujin that seem to go against this ethos, and I somewhat agree at the contradiction, but doujin are viewed as a derivative expression of fandom and not a modification of the original work of the creator and passing it off as the “better version.” That sort of act is viewed with this level of disdain because of the implied arrogance that the modder both 1) assumes they allowed to do what they are doing with impunity because they judge it to be better, 2) are releasing it for others.
Finally, there is a huge difference between doing something and releasing something. The line here is clearly releasing it to others. That is the tripwire. And to be honest, I can see it both ways. If someone decompiled Bayo 2 and put it out on PC, I think I’d be pretty miffed. Nintendo saved that game with their money, and to do so would create a negative business environment and damage their future prospects. It’s their game to exploit. Just like Namco could do a PC Tekken collection with online play. That would be their choice first; not the arbitrary choice of a modder. That right is reserved by the original creator.
Not saying folks have to like it; there is a strong argument for preservation (without distribution) in some cases. Adding and distributing non-shipped features does seem to cross a line though. So I get it.