JAL and ANA really love their old 747s and JAL has kept their DC-10s for a long time. One example that comes to mind is the only existing 747-100 EUD operated by JAL. As an enthusiast, I think it is great that they keep these aircraft around. I have wondered though why they do it from a business perspective? JAL and ANA have long been protected by the government. Air fares were until relatively recently, government controlled. The airlines could have persuaded the government rather easily that they needed to keep their fleet updated and thus needed to keep fares high. I think Japanese carriers also have low capital costs so they could get the financing without a problem. Even most US carriers which tend to push aircraft towards the end of their service lives have dumped most of DC-10,L1011, and 747 classic aircraft in service. (Of course, I know NWA still flies 10s and 742s). Further, a lot carriers in the region have all nearly new fleets- KE, OZ, SQ, TG, MH and so on.
I suspect that airplane enthusiasts have some role in the decision to keep these planes in service for as long as they have. I know these planes are paid for. But it seems that maintenance and fuel savings from new aircraft would have offset that advantage. Does anyone know or have a guess that is better than mine?