There are some basic differences that may play into it. The OR fish don't have the Salish Sea, they go straight to the ocean similar to ort north coast stocks. In conversations with their bios, at least some of the streams are naturally productive due to the base rock, which makes them less dependent on salmon to deliver nutrients. I am not sure if OR had the massive Chambers Creek style management with the really high harvest rates and genetic influences. I don't think that OR has the intensive net fisheries on all the steelhead systems. Lastly, further conversations with bios down there indicates that repeat spawners are more abundant in OR than WA.

One might also want to look at the amount of effort, the amount of development and size of communities, and such.