Because that is the method that the law allows, the areas are set up and fully funded and operational. ODFW and WDFW have increased the number of smolt to these SAFE areas.
It satisfies the public right to the fish.
It would create an instant bridge to whatever harvest method that is developed in the future.
And last but far from least, it ends the status quo by eliminating the effects of gillnets in the mainstem.