And what's the 'breaking point' for advertising? If they spend $100 on advertising and somehow figure they received $100 as a direct result of that advertising, is that a win? Do they need to receive 10% more $110? Or 100% more, $200. I'm sure there's a guy with a pocket protector somewhere who has the magic formula at the ready.
don't forget that private/public corporations write off the sponsorship cost as advertising .... consequently, they get to use money to advertise their company instead of sending it to the government .... that alone is a strong motivator