I believe the Vuelta was moved a week earlier in 2011 to move the Worlds from October to September. Thanks to this they had better weather in places such as Bergen or Harrogate.Btw, why is the Vuelta so early? It starts two weeks earlier in 2021 than it did 10 years ago. And the race calendar after the Tour is really strange. There is next to nothing happening after the 5th of september except the Worlds and Il Lombardia.
The extra week this year also applies to the Tour, so I guess is because of the Olympics.