The basic intuition underlying rewards cards as a product is that highly desirable customers have options in how they spend their money. You can directly influence them to use your rails by making those rails more lucrative, more fun, or both for the customer. And so card issuers (and the networks) compete with each other for so-called “share of wallet” by bidding with interchange.
Almost everybody writing about credit cards on the Internet receives some sort of spiff if you sign up after clicking through tagged links in their material. That is not my business model (people pay me to write about financial infrastructure), but is probably one you want to be cognizant of every time you read about credit cards online.
https://www.bitsaboutmoney.com/archive/anatomy-of-credit-card-rewards-programs/