I think it's more the Italian mentality more than anything else
To some degree, but you also have to look at the individual teams and judge that for yourself.
Look at Inter, with Santon and Balotelli. Granted, santon isn't getting a great amount of playing time, but he has certainly played a good amount of minutes considering how young he is. Balotelli has a tendency to explode and implode on the pitch (in a good and a bad way) every time he steps onto the field.
Roma has always had a policy of promoting their youth and playing substantial minutes. Partly due to finances, but also because they have a great history of nurtuting young talent.
Even Juve in the past with bringing in Del Piero, Tacchinardi, among others.
If the palyers are good enough, then they will be brought up and given playing time. They were both teenagers when they first got on the scene, and were playing right away.
Maybe these kids being brought through the system simply aren't good enough? Or maybe, just maybe, they should really go back to taking these financial risks that they did when they purchased the likes of Del Piero, Zambrotta, Tacchinardi, when they were purchased before the age of 22 and in the cases of DP and Alessio, when they were only 18.
I'm just trying to think of the last truly great Juventino who was brought up through the youth system, and right now it escapes me.