Why don't they play stadiums?

[FuzzyPlum]

I was wondering that.
I guess its only now they have been in a position to sell-out stadiums. I'm not sure what it has been like in the US but the London shows were added gradually. Not sure whether were always likely to play those dates or whether they just got added 1 or 2 at a time as demand dictated when the shows sold out. Perhaps knowing they can sell so many tickets would make them consider stadiums in the future.