This maintenance window is required per the CBA (Collective Bargaining Agreement) between Activision-Blizzard and the SHUIU (Server Hamsters United International Union).

There is going to be a huge load on the servers come the launch of Shadowlands, and this is the last real chance for Blizzard to service the hamster wheels, ensuring that they are properly balanced and the axles lubricated for low resistance spinning.
In the meantime, the hamsters will be getting the last chance to binge on carbs, visit with their families, and get their last mani-pedi’s that they’ll be able to get for months. Don’t begrudge them such small benefits for us to be able to play the new expansion.
/moo 