Adidas makes most of the money from Man. Utd. There's no marketing or economical reason to stay at Juventus when 2 economical powerhouses offer you insane wages + exposure + image rights. He simply can't have that at Juventus yet. Our club needs to focus more on developing marketing strategies so we can become more recognizable brand.
Pogba clearly doesn't want only to be best at football, he wants to be n.1 sports name in the world, and that's something that is only achievable at someone who's one of the best at it: United + Adidas.