I think they key is that in your example, Cosco/Walmart was "buying" from the company and is now "buying" from a competitor. Google's typically not "buying" from anyone when they choose who to list on their pages (only "selling" exposure, in cases of paid advertising).

There is a business relationship between Walmart/Costco and the product or a competitor of the product. In the Google News case, there is no business relation with any news site (Alphabet ads might have a relation with the news site, but that is not Google News).

Google News is a customer who walks into Walmart consumes the free samples and tells people about them.

Walmart is free to ban Google from the premises (robots.txt) or to negotiate an exchange (monetization agreement).