I have to believe it has mostly to do with their commercial worth......

Most commercials wont mess with them, and if the Tribes could get top dollar for them it would be a different story. After all, if subsistance is the main reason for treaty fisheries, why do they not take more Pinks than they do?
They smoke well, can even better (but who likes canned salmon that much?), and are very plentiful.
Of course the other scientific reasons have merit, but I still say it has mostly to do with how much they can bring in $$...... Not much, so they are plentiful....

MC