I think it's a conglomerate of factors, including WDFW bending over for the tribes and commercial interests. Habitat destruction (logging is a big culprit and destroys spawning habitat), tribal fishing, commercial fishing, sport fishing harvest (although a drop in the bucket compared to tribal and commercial fishing), ocean conditions, and poor management all factor in. It's hard not to envision a complete shut down of salmon and steelhead fishing with the way things are going. Which is a shame. However, not entirely unpredictable.
Humans have been on the planet a short time but have managed to really mess it up.
You're not entirely wrong. WDFW does not advocate for recreational fishing in western WA anadromous waters. The reason, aside from not giving a shit about you and me, is that the Dept. will do whatever the treaty tribes tell them to in order to have NT recreational salt water fishing seasons for salmon. So recreational salmon and trout fishing in streams gets thrown under the bus. That's reason number one. The second is that the governor prizes tribal cooperation more than the other 98+% of WA citizens. That trickles down through the state agencies. WDFW acquiesces to NT commercial fishing mainly because the seafood processors lobby the Legislature far more effectively than sport fishermen do. It amazes me how cheap it is to buy a state senator or representative.
Additionally, it may help to understand WDFW's priorities.
1. Preserve all FTEs (full time equivalent employees). This is basic to maintaining and growing a bureaucracy.
2. Preserve and expand the agency budget. This is essential to #1. So taking your tax and license fee dollars and giving you little or nothing in return is just the process of fulfilling the agency priorities.
3. WDFW is first and foremost, "The Washington Department of Salmon." Let there be no mistake. Even though WA salmon harvests are but a small fraction of what they were 30 years ago, the Dept. continues to spend more money on salmon hatcheries than anything else by a significant margin. Combined with the money spent on salmon management, that returns far fewer salmon to recreational creels than it does resident trout to recreational anglers, salmon is where the money gets spent. Money for trout and game hunting almost look like a budgetary after-though by comparison, even though most of the Department's budget comes from taxpayers who mostly don't hunt or fish, although hunters and anglers both pay taxes and buy licenses and permits.
4. Harvest of fish and game is co-equal with preserving and perpetuating the state's fish and game resources. The Dept. has more direct authority over harvest than it does the habitat that preserves fish and game populations. So that's why we see more emphasis on harvest than preservation.
Habitat degradation has slowed down significantly due to the many environmental protection regulations. However, degradation still out paces habitat preservation because the ever-increasing human population require space and resources that consume and degrade habitat. Since that is Debbie Downer kind of news, agency policy wonks and politicians would rather you think that we can have it both ways, preserving fish and wildlife and accommodating human population growth. They're wrong.
There is a lot of complaining about the effects of tribal and commercial fishing. For the most part, neither contributes very much to reduced productivity of salmon and steelhead populations in the last couple decades. Mainly it is that fish caught by tribes or NT commercials are not available to be fished for by recreational anglers, which is a very different thing. Allocation is not the same as reduced fish populations, although the effect on sports fishing is often the same.
While freshwater salmon and steelhead habitat continues to be lost at a slow rate, the ocean survival of salmon and steelhead smolts to returning adults has crashed at a very rapid rate. That is the main reason recreational steelhead seasons have been curtailed. The other reason for freshwater stream closures, of course, is the previously mentioned demand by treaty tribes that WDFW close them.