When you send a player to Serie B, you're in all likelihood sending him to oblivion, unless the team campaigns really well and win lots of games.
Otherwise, the guy gets surrounded by mediocrity and it gets really tough to stand out.
Actually the same is worth for loaning out to shitty Serie A teams.
The point is a talented player who struggles in Serie B or in a shitty Serie A team wouldn't necessarily struggle playing for the main Juventus team, in a reduced role. It would be actually easier, specially depending on the player's characteristics. I guy like Soulé, for example, if loaned out to a mid Serie B team, would probably disappear to never be found again.
So basically, the way to really develop youth is in the first team, as it's happening now - but it's happening as an exception, because of injuries and the poor quality of the squad. They really should learn from this and start actually putting more trust in youngsters who have shown potential. We've been saying this forever, and this is the reason Italy doesn't develop more talent. They have too little trust.