It's US law.
If Kellogg doesn't defend their trademark, they lose it.
An amicable middle ground might be for Kellogg to let the business purchase rights for $1, but if that happened it would open up a flood of this.
Kellogg has so much money in that brand recognition, they'd lose far more than $15 million if it became a generic slogan. The $15 million is a token amount to get the small business to abandon its use. Kellogg doesn't want to litigate. They tried several times not to litigate.
I'm sure Kellogg would be happy to pay the business more than the cost of repainting their truck, buying some marketing materials, pay for the trouble, etc. It's easy good will press for Kellogg and the business gets a funny story and their own marketing anecdote. It's cheaper than litigation, too.
Did Kellogg actual win according to this supposed law you cite? Did they prove that their trademark was used?
Or are you blindly guessing?
this isnt a great law though.
a non competing pun ahould have similar carve outs to fair use, to save both the trademark owner, jokester, and courts a bunch of time and money.