WoW still has server problems - why do you think they have to reset the machines every week.
While there are definitely software issues to solve, you have to understand the majority of the maintenance windows for WoW are used to conduct hardware repairs. They have literally thousands of servers and god knows what kind of NAS setup to maintain. Hard drives die, motherboards need to be replaced, disk controllers fail, etc. That happens every day but it rarely affects most of us on a regular basis because our scale of ownership is far lower than an operation like WoW. This is to say nothing for expanding on that hardware solution, network infrastructure and etc. For such a huge operation that requires nearly 24/7 uptime, I'm surprised WoW doesn't have MORE downtime.
And I am not a fan of WoW for the record, just saying it's perfectly understandable from a tech perspective.
Playing: Risk of Rain 2, Jedi Fallen Order, Last of Us II
Watching: Tenet, Peninsula, The Pale Door