Legally binding is a nebulous concept when you're some of the world's richest companies with legal departments multiple times larger than the entire staff of the companies you're 'legally bound' with.
The flip side of being rich enough to hire good counsel is being rich enough to be worth going after. Were Google to renege on an agreement such as this, there would be a line of litigation financiers standing to buy the claim.
"Taking this to court will cost you a bajillion dollars. And you'll lose. Cut the antics and pay them off."