That's a very loaded question. Truth - its probably a combination of all of the above in conjunction with other factors.
If you ask locals, they will probably entirely blame environmentalists, forest service management, and the Mexican spotted owl. If you ask the forest service, they will say that it's because the old growth trees have already been logged and it's not economically feasible for the logging companies to harvest the smaller trees.
I think the truth is somewhere in between. It takes a long time for Ponderosa Pine trees to mature in that area. And decades of over logging, followed by overcompensation of environmental restrictions, plus increased cost of labor probably meant it was more profitable for logging companies to work where it was cheaper - overseas or in more heavily forested areas that receive greater rainfall and faster tree growth.
EDIT- sorry, I noticed you were asking about the reservation specifically. My response was more geared towards forest service logging. Much of the same holds true for reservation lands - but replace federal restrictions with tribal politics.
Edited 1 time(s). Last edit at 08/30/2016 11:25AM by MSRRKevin.