The retired passenger airliners work well for the package operators as acquisition cost is low and airframe utilisation is far lower than in passenger service, so higher fuel burn is not as big a deal. Plus the industry has various peaks and troughs so they can be parked up when not needed, or flown with even lower utilisation.Looking at your pic Bryce, amazing sales must be also achieved by aircraft manufacturers just for freight.
I’ve also heard that many outdated passenger aircraft spend many many years after being retired from passenger service as freight aircraft.
Amazon stated their own airline a couple of years back after they ended their contract with FedEx. It’s based on old 767s, converted from passenger service. They contract out various operators to fly the aircraft. They have 50 of them with an average age of over 28 years old.