Agree with the other posters , these older generation jets aren't economic for high utilisation scheduled cargo ops. For ad hoc charter or other ops where the utilisation is low and the aircraft is waiting on the ground a lot the lower capital costs make sense and they are still good in that role.
There is another problem: C & D checks, landing gear, many components are calender-driven on old machines, so if you are on low utilisation, maintenance costs per hour becoming very high, I think most remaining operators of those old aircraft are not considering to do next D check, just scrap or park the airframe. Again CPCP, aging aircraft programmes and some ADs making them not viable for "developed" countries operations, but with some sort of creative approach and buddies in Kinshasa CAA some people still can make money out of it.