There is a school of thought that feels wild fish are more aggressive and therefore more apt to take a fly than hatchery fish. Therefore its best to fish barbless. But I agree with the idea of killing all hatchery fish landed. I would assume the limit is so that more anglers are able to enjoy taking a steelhead home for the barby or the smoker as it still some of the best table fare I know. I've not fished the Methow for steelies but I would thing most of the fish landed are fairly dark by then but still need to be harvested.