Bilt Rewards Vice President Richard Kerr wrote up an in-depth explanation of travel portals. Bilt uses Expedia for members who want to redeem their points at 1.25 cents apiece towards paid travel, whether it’s hotel or airfare or other bookings.
American Express, Chase, Citi, and others have travel portals and it’s common to use a third-party ‘white label’ service like this.