Juventus is a complex system that requires managers capable of managing it. Allergi and Marotta, regardless mistakes they made, were of the required kind. Sarri and Paratici aren't. The problem is that the lack of competent managers is a general problem of the modern world of football (well, not only football, but let's keep it within the context).
The situation is really bad for Juventus right now: the entire management squad has to go, but there's nobody to realistically replace them with unless the club is ready to spend big, which is unlikely. The entire situation smells really bad, and the worst thing is that they destroyed everything they had built with their own hands.