Probably because since 1999, these are his managerial terms: -That’s why I don’t understand the shouts that he’s not a long term manager, he reinvented that Milan team a few times and kept them competitive.
Juventus 1.8 years
Milan 7.6 years
Chelsea 2,5 years
PSG 1.5 years
Madrid 2.5 years
Bayern 2.5 years
Napoli 1.5 years
So in 7 jobs in the past 20 years, only 1 has been for more than 2.5 years, so Milan is very much the exception.
If he stays for 3 years, it would only be the second time he's done that since 1999.