It's desperation. Remember kishi knows he has lost most of his fan base because he destroyed the story for the end pairings. But the problem is he can't just say kitten it and not put any effort into this gaiden. Since we know how important Naruto's sales are to several companies because it was their biggest seller for years. They also believe that Naruto had international appeal that one piece just doesn't have. Which is probably one of the reason kishi is given a chance to make this gaiden and the movie because they hope he has some sort magic touch that will draw in the fans and make them a lot of money that SP and editors said The Last would bring them if they made nH canon. But like i said even by this point he knows he lost his fans because of the ending but to prevent from losing his job, and being able to continue working he needs to show that he can still draw in the fans. But the story was destroyed for the pairings so he has to make the plot pairings related. It can't be about nH or Bolt because the nH fans showed how much they support the series when they were given what they always wanted. So it had to be about SS and it had to be about Sasuke because he one of the most popular characters, and SS is one of the most popular pairings in Japan.
IMO. This gaiden wasn't supposed to be written.
It's here because EDITORS asked Kishimoto to do it to try to end the hate from the fans.
They want to try to make us accept what we don't, and they wanna try to stop the hate.




















