Real and Barcelona already spent a lot and can't buy new players, Juve don't need him and if he don't want to go to China and retire there, he have no choice but to stay in ManU.
Well Everyone needs him if they can sell other players.
In real Barca or Juve, he will be better than actual players so he will be needed on every team.
For example neither Messi is needed at Real but if he will go he will play and they sell another one, even hazard for him
In my opinion, Juve already have very strong team and not sure if they really need Pogba.
You see, it's very difficult to achieve team unity if you have more than one "big star " in the team.
Very good example is Paris SG last year.
Juve should build their team around Ronaldo and if they bring another star, Pogba, not sure if this will work.
You can't have 2 leaders in the team unless you want to see conflict like in Paris, ManU etc.
Personally i don't think that Juve will get Pogba, considering the price Man Utd. asks from him, last i heared it was 180M euro and he is definitely not worth the money.Even Reak has issue with that amount.And afterall, that money can be spend better.
Don't get me wrong, he is very good player, but in my opinion not a game changer and he won't bring Juve CL trophy, and they are after that.