I don't think they're tougher although there is definitely a strong omerta culture in Corsica.

I think it has a lot to do with the fact that this option didn't exist until recently so there was simply no choice of cooperating. Even if someone wanted to cooperate, the French justice system had nothing to offer him and would not have been able to "handle" him from an legal and administrative point of view.

I think, once the Corsicans will see that this option is working, they will start consider it and i wouldn't be surprised in the near future if one or two high level Corsican guy decided to testify. It would be very interesting because the inner working of the Corsican mafia is still relatively unknown.