Sure there is a little bit of fanfare going on, but more importantly there's a difference in presentation and technique between drifting, nymphing and the more traditional spey approach that shapes the proper fly for the technique. Let me explain my point of view FWIW:
In the original act of salmon angling in Europe it was a swinging game. Salmon flies were aptly designed to swim, not drift along with the assistance of weight or floats. The gut eye, properly proportioned wing and body, even the collar and palmering were as important in function as they were 'expressive' in form because they made the fly ride throughout the swing in a manner that solicited the fish from their lies to take the fly, to move the fish to the fly rather than move the fly to the fish. Did they get carried away with the choice of materials? Hoo yeah. But it created a legacy that is an important part of angling lore.
Upon arrival in the new world, the hard to find feathers may have largely been replaced with hairwings, but not much else had changed. The fundamental design of the salmon fly and dee/spey fly had no reason at all to change due to the presentation style from Newfoundland to Maine. The availability of mallard and the generally humble dress of spey flies compared to classic mixed wings made them easy to tie on anyone's budget. Yet simpler hairwing versions of classic salmon flies were the dominant direction and remains so today.
Despite rare feathers adorned on the full dress salmon flies, they swam right and caught fish. Some color schemes would in fact work better than others at certain times or in certain rivers, but to your point most of the materials could have been replaced, omitted or otherwise ignored but not the design has been proven to be effective for centuries. Nonetheless a swinging fly design is lost on drift presentations, just as drift flies do not work well on the swing.
Look at the popular flatwings with jungle cock eyes for stripers, fished on floating lines. For the mentality of the fish being sought this is way more extravagant of an offering than a spey fly for an atlantic salmon or steelhead who is not feeding! Yet people think nothing of getting all fancy for stripers, the thick shouldered blitzing linebackers of the suds. I found out years ago that a blob of epoxy on a hook will take even the most finicky stripers. Yet I too get frilly with striper flies now and then.
Anyway, a century or so ago the wave of salmon angling lore hit the pacific northwest's steelhead rivers and the result is by and large the game is to swing if you are a fly guy. Chuck and duck, indicator and nymph, etc - are the exception rather than the rule for fly rodders out west vs. GL where it is the rule. I attribute this difference to the fish, the fishermen, and the conditions. The fish out west are probably more willing (wild), the fly-fishermen more patient and less focused on quantity over quality, and the temperatures are warmer which supports the two previous observations. There are serious flyguys, and serious gear guys using non-fly rods and tackle, not gear guys using fly tackle.
I could be totally up my kazoo but I have fished both and have formed an opinion based on watching the masses fish over redds with guides in the midwest and comparing this against the steelhead culture of which I partook for many years.
(Back to fly design) neither an egg fly or nymph will swing well, although the ol' wooly bugger gives any fly a run for the money.
It does not belong on the same list as the egg fly and nymph fly because it is a wet fly that swims and is effective on the swing. It's design is very similar to the European tube flies, but there is no tube. I've caught many steelhead on the swing with buggers. Some funny fish stories behind that. Anyway nymphs and egg flies swing sideways and upsidedown, they are designed for drift fishing or under a bobber, for instance - or behind some split shot etc. Spey flies are designed to swim enticingly in an upright fashion, and yes they do solicit strikes as they did centuries ago.
In summary these are just the observations of a dedicated steelhead angler who has seen both sides. For me it boils down to this - one day spent in shirt sleeves on an early fall day grease lining a spey fly in caddis colors just under the surface film on a floating line is all it takes to savor the swing... then a chrome bright summer steelhead torpedoes the fly and the serenity is shattered into chaos for a while as the fish who was bold enough to rise to the take flexes it's acrobatic muscle and your ears ring with screaming drag. It's a native... be gentle and pluck the barbless hook from it's jaw so it can swim free. With practice, the swing techniques become effective for the angler and the reward becomes the achievement, not the fish - IMHO. Hence the traditional fly design's popularity in steelheading.