They have so many Mi-17s and variants in service and they've probably built up such a large support network for the helicopters that it's probably more effective just to keep using them. Hell I expect the PLA to keep buying Mi-17s alongside Z-18s and Z-20s because Z-18 and Z-20 production rates won't be enough to satisfy the combined demands of army aviation, naval aviation and air force.
However I do expect and hope to see older Z-9s and Z-8 variants eventually being retired.
However I do expect and hope to see older Z-9s and Z-8 variants eventually being retired.
