As others have said, there's a bit more going on than just the game being patched.
Datacenters are being serviced, if I am not mistaken they are shortening the positional delay on certain battlefields and I am pretty sure extra server capacity needs to be added to accomodate the new dungeons, housing, Wolves' Den, etc.

That said, where have you been?
It's been announced nearly or even over a week ago that this would be a big maint which would take ~24 hours.