Apple's new campus for example is basically a landscraper.
Apple's lot in Cupertino is approximately 2400 ft by 3400 ft (although it's trapezoidal, not rectangular). For comparison, that's roughly the entirety of downtown Providence. Or, superimposed on Manhattan's grid, 9 streets by 4 avenues. It's roughly the dimensions of the elevated loop tracks in Chicago.
The Empire State Building occupies 1 street by ½ avenue. Sears Tower is on a lot about 450 ft square (one slot in the Chicago grid system). You just simply can't acquire the land in cities that you would need to build landscrapers.
Except, the OP case is London, which has some of the most expensive real-estate prices on the planet.
Not that I disagree with your overall point, just this final statement doesn't ring true.
Let me check the bottom of my purse. Just a little bit short (measured in decimal places, about 8 of them).
TLDR: this landscraper is Google's way of storing/investing it's offshore cash, at it's heart it's a tax dodge (funny how it isn't mentioned in Mr. Khan's comments that a LOT of companies in London are in fact there purely as a tax dodge).