I assume it's because it's less easy to game, rather than say "oops we made all our money in Switzerland that year".

Big companies make a habit of pushing their tax liabilities to the most favourable jurisdiction. As the other comment said, they would take the piss.

Also, it is worded to say that it's 4% of global revenue for your parent company.

So there is no setting up an offshored tiny company to wear the liability - your parent company is on the hook, wherever that money may reside.