I’ve gotten value from Thanks Again earning miles for years, just a few at a time. They started out with brick and mortar retailers and I’d earn points when I least expected it. Then they pivoted to focus largely on airports.
When you go through the airport you’re the airline’s customer, and the airport rarely knows who you are. But the airport makes money when you spend money at retailers there. So by rewarding that spend they learn about who their best customers are can provide even greater rewards.