One of the most obvious explanation is that 95% of the Italian top athletes have a salary from different military groups. We have Fiamme Oro (Civil Police), Carabinieri (Military Police), Aeronautica (Air Force), Fiamme Gialle (Custom Officers), Fiamme Azzurre (Prisons), Esercito (Army), all groups that give a salary to the recruited athletes of different sports, same level of who really works in the various corps.
In a period where the possibility to have a job becomes a problem in the most part of the European Countries, athletes having a salary for a job in some sport discipline can dedicate all their time to training at max level of commitment, if have great motivation.
But also the different organization (comparing with the past) of the technical development and assistance plays an important role in this explosion. Some year ago (6-7 years) FIDAL decided to name Stefano Baldini as Technical Director of all the Teams (Under 23 - Under 20 - Under 18) while Elio Locatelli was the responsible of the ELITE athletes only.
Some athlete was already in the ELITE group (Tamberi, some of the walkers, Jacob as long jumper, Donato triple jumper now coach, and some few others of high level), but this organization that for young athletes involved their coaches too looked at the "decentralization" instead at the "centralization" we had before.
When I was the Technical Scientific Director in Italy, in 2002, I already made the project of the decentralization for growing coaches technically supported by the National Responsibles of the various sectors, but the Federal Counsil didn't approve the project for administrative reasons, and this was the main reason because I resigned from my role.
Fifteen years later finally the Federation started the project, increasing the budget of the Technical Sector, that in 2000 was no more than 25% of the total Federal budget, and now is around 57% of the total.
These are the reasons, not doping or something strange : more money, more motivation for personal coaches, creation of small groups of top athletes in the same discipline around good coaches, and possibility for every athlete to chose the best coach for them, also abroad (Jacobs with Rana Reider, the pole vaulter Roberta Bruni with the cuban coach of the Olympic Champion Silva, Di Lazzaro in Spain, and many others), while some Italian Coach instead was chosen by foreigner athletes (the British group with Marco Airale in Padova including Neita, Azu, Prescott is an example, Sandro Damilano coach of Chinese walkers another example, for finishing with the strange my situation with a group of Marathon runners including the German Record Holder Amanal Petros, the Swiss Record Holder Tadesse Abraham, the best british Emile Cairess, Zerei Mezngi from Norway, and the best athletes from Uzbekistan, Shokhrukh Davlyatov, plus of course Kenyans and Ethiopians).
The reality is that, in the athletics of today, 95-98% of the activity is individual and personal, and the Federations using the old system of centralization (practically ordering to the athletes what they had to do, so the athletes as "service" for the Federation) don't have anymore power with the strong domestic athletes. The role of a Federation, looking at the eviolution of the Society, must be to be the "service" for the athlete, not the opposite, with the main task to discuss, but to support, the plans of every athlete and their coach.