The idea that Cargo crew can not find a job in a Pax company is mostly totally wrong. Almost all Cargo crew has flown pax. before . cargo Night freight is the most demanding branch of commercial aviation, you do need to be at the top of your game and sloppy operators have no place in a night freight operation.
Cargo crew have more DGR's to cope with, need to check the correct loading of the aircraft ( all too often not done unfortunately, also amongst UPS,DHL,Fedex and TNT crews), fly with indeed often older equipment during the time of the day that your body needs sleep instead of work. It is therefore normal that Cargo crews ( and I am talking medium and widebody Jet) are paid better than their Passenger hauling colleagues.