I think finnish cmore analytics gave the answer:
Jari Ketomaa said that Pirelli's studs are installed when the melted rubber is casted so the studs won't get off.
Riku Tahko said that normally when the studs go off you know the tyre is not good anymore and you need to slow down cause no grip.

When you think about those two analyses you get the answer.
The studs don't get off since they are casted and the driwers won't slow down so the the tyre just gets too much stress to the lamination
so that peels off.

EDIT: I'm not an engineer so this can be way off the truth.