>>717300647 (OP)
1. Whenever someone mentions this for One Piece or Hunter x Hunter, you get a flood of faggot anons who claim the only appeal is in the preexisting characters and they would refuse to play the game if you made your own character and didn't follow the story. Publishers hear them and agree.
2. Developers agree. The only reason you, as a video game developer, would make a game for some other dude's IP is to bait preexisting fans into buying your game. As such, it doesn't behoove you to make a game without the familiar characters and story. You also probably don't have the budget anyway. This only is maybe possible if the suits who own the IP also own you, since you don't need to pay licensing fees then.
3. Even most authors who spend a lot of time on worldbuilding and selling their readers a power fantasy, like what you see in battle shounen, still acknowledge that their work is a story and as such has a beginning and an end. This means, by the end of the story, they tend to leave very, very little room for anything meaningful to be explored. Writing a new story in that world then becomes troublesome as you're constantly hiding under the shadow of Ninja Jesus and the Greatest Conflict Ever Told Ever.
Granted, you can always squeak something through. The Naruto world is pretty big, the story covers a short period of time and your own story doesn't need to reach the same absurd power levels or geopolitical relevance. There is still, however, the specter of canon that forces you to artificially restrain your story. You can't contradict canon, you have to be mindful of where canon characters are and what they should be doing at all times, etc. It's just a huge pain in the ass.
That said, it's easier for some series to get away with this than others. For example, if you look at JoJo's Bizarre Adventure, you could remove a part and not notice anything really absent reading the other parts. So why couldn't you insert a part?
