What makes you think that nobody can get the billion?
Insurance policies require you to pay a certain amount guaranteed, then pay back a much larger amount if something unlikely happens. So Pepsi had to pay $10 million. If the right thing happened during the game then Berkshire Hathaway would have paid a billion, and some lucky consumer would have walked away a newly minted billionaire.
wouldn't actually giving out the $11mi to the consumer, or picking 10 consumers, create more brand awareness than promising $1bi that nobody can get?