I feel like folks like us, that never miss a payment, and max out our rewards, are net-losses for most credit card issuers. It's not clear why they don't just fire us as customers.
They can also earn money from retailers to promote them to you. Point hunters often end up spending extra to reach a rewards threshold, which can be very profitable for the retailer. It's also common to sign up for a card with great introductory rewards and then keep using it for years, because you get busy and forget to switch card every few months.