Official announcement by the vendor Volantio was yesterday; the practice has a name..."Post-Booking Revenue Management". It's like the secondary market for concert/sporting event tickets

"Volantio’s platform assists airlines in identifying high-demand flights within a week of departure. It then helps airlines craft and deliver offers to passengers, working to balance demand. Passengers are offered flexibility to change their trip, and sometimes a reward (often a travel voucher, similar to a bump at the airport) to make that change. The airline is then able to sell that in-demand seat, typically at a higher fare."

https://paxex.aero/southwest-volanti...ue-management/