Obviously, because they're in the Champions League at this current time and we're not. Pogba will be tempted by Mourinho as manager, playing with his friends Martial and Schneiderlin, the huge wages and playing for one of the biggest clubs in world football.
When it comes to Juventus v Man Utd, there simply isn't any comparison. We've got a bigger fanbase, bigger stadium, famous manager and can offer far more in wages.
It's a no brainer UNLESS Pogba wants to wait a while for Real Madrid to come calling. Either way, he won't be at Juventus long term. Serie A is tier 4 these days with the very best players preferring La Liga, Bundesliga and the Premier League.
Serie A, in general, is a retirement home.