I've been thinking about this one for a bit...
Basically, a normal MMO tends to have the majority of the players on during the weekend.
If the intention of the maintenance is to provide as clean a slate as possible for players, why is the maintenance not run on Thursday? If quests clear up like acne after a maintenance & tend to fail over the week, why perform the maintenance after the majority of the players are done playing for the week?
By "done playing for the week" I mean the logins are not as frequent. ie, I work 40+ hours a week and most of the week, all the time I have in-game is to do dailies. The weekend is where I tend to play "for real".
tldr; Things tend to get broken throughout the week, so why is maintenance not performed right before the majority of players have play time? Thursday or Friday