My guess would be a vehicle came and scared them off. Otherwise, they'd have taken the other backstrap and choice rounds too from the other side.
I believe all of the tribes, as well as nontribal regs, prohibit waste. Still happens. Most of the oriental market velvet antler hunting happens June-August, when the velvet is still on and the antlers full of blood - that is when they are most desired. Top dollar velvet antler has most of the beam growth but still lumps, rather than points, at the terminal ends.
Not racist to understand that the tribes have hunting traditions, many have been corrupted by drugs and alcohol, and will do almost anything for a few dollars that doesn't involve holding a job. Obviously, not a problem restricted to the tribes.
As recommended above, report to WDFW.