The extended maintenance days are mandated rest times per the CBA (Collective Bargaining Agreement) between the SHUI union (Server Hamsters 
United International) and Activision-Blizzard, which transferred over to Microsoft.
Those poor hamsters work their little hamster butts off for us, and the least we can do is give them some extra downtime on content releases because they will be working extra hard and longer hours in the coming days and weeks as players rapidly consume the newly added content.
The extra down time for the hamsters allows them to get deep tissue massages, mani-pedi’s, and bottomless mimosas for the hard working server hamsters.
I have gone to great expense and personal risk to obtain footage of the real behind the scenes going on during extended maintenance. The following is not for the faint of heart:
/moo 
