Check the best 10-15 teams in Italy and tell me how many of the Italian under 24 players have an important role in their clubs.
Criscito, Bonucci, Giovinco, Ranocchia, Abate, Sirigu, Schelotto, Astori,
Candreva, De Silvestri.
If we are talking about guys like Biabiany who were hits in the provinces but bit part at the big clubs then I could add Lanzafame. Depends how you choose to look at it. Guys with top flight experience like Okaka, Cerci, Paloschi.
If I add in Santon, Balotelli, Macheda, as inevitable Nazionale it adds up.
If you lift it one year to the comparatably veteran 24 you are adding a lot more players (Motta, Santacroce, De Ceglie, Marchisio, Pozzi, Masiello, Viviano). Whether they are good or not is a different issue, but it's not some doomsday scenario, just sheer competition.
Going over old ground again and again, but the lifespan of a footballer in Italy is different to many countries, it starts later and ends later. That's the system, the Primavera runs up to 20 year old players and then they get loaned, only 'wonderkid' players generally break that mould. No one is denying the system is also a big issue. Spanish sides for example have three big advantages;
1) Ethos on home grown players so they bring through a lot of talent for their home national side. Something that many here would rather abandon in favour of signing talented youngsters regardless of nationality.
2) 'B' teams in a professional league.
3) Non-EU restrictions on match squads.