Inter don't want to be obligated to buying Udinese's half for 9m. So while Juve could sell their half, Udinese would continue to want 9m for their half of the player. So whether Juve want it or Inter, is not their problem. This is where the deal is getting bottlenecked.
Personally though, I'd prefer holding on to the player and getting Kolarov for the left rather than Zuniga.