Oh Josh, I can't believe you'd start this shit up! First off, most of us did NOT start off with a 9' 5 wt unless we're your age or younger. Sheesh, damn kids nowadays anyway. In the days before 1980, or 1970, the single rod quiver was a 7 1/2' or 8' 6 wt in bamboo, followed by fiberglass in the same length and line weight. That would have been the all around trout and panfish rod recommendation in fly shops (what few there were) and sports shops, coast to coast. Then, with the advent of graphite rods in 1973 it took some figuring out that a longer rod could be just as practical in the same line weight. By 1980, Kaufmann's fly shop catalog was recommending a 9' 6 wt as a first rod and all around trout and panfish fly rod. I'll add that Orvis offered an 8' 3" 7 wt graphite rod they named the "All 'Rounder" for everything, trout, panfish, bass, and Atlantic salmon. What a morphadite rod that thing was.
By 1990 fly shops had become commonplace nationwide, fueled by the YUPPIE boom (young urban professionals) toting their VISA gold cards into shops everywhere. I add this because until around 1980, full service fly shops were a rarity, except in key locations like West Yellowstone and thereabouts. In those times of yore, outfitting one's self as a full fledged fly fisher required a fair amount of leg work. Meaning you'd go to one general sports shop for a set of Hodgeman or Marathon waders, another for a fly rod, and possibly yet somewhere else to find a fly reel other than a stamped aluminum cheapie or Pfueger Medalist. And then wander around looking for flies wherever you could find them. A lot of fly fishers took up fly tying just to secure a reliable source of flies. And fly tying materials were scrounged from many places, which made a store like Patrick's Fly Shop on Eastlake in Seattle such a gold mine. Patrick's originally sold only flies and tying materials, no rods, reels, or waders. This is why the good fly fishing waters were relatively uncrowded. It took a lot of gumption and resourcefulness to go fly fishing effectively. But the YUPPIE boom and VISA Gold cards changed all that. Full service fly shops proliferated. You could walk into the new fangled full service fly shop, lay your VISA Gold card on the counter, and walk out fully outfitted from head to toe as a NEWBY fly fisher before ever getting your first fly casting lesson. And fly rod companies went ape shit, meaning that by producing a bountiful supply of fly rods, fly rods became better than ever imaginable. So by about 1990, shop recommendations and popular demand settled on the 9' 5 wt graphite fly rod as the nearly universal introductory all around trout and panfish fly rod. Of course it didn't do everything. Still doesn't. But it does more things than any other single wt rod does. Ask the rod companies; their production receipts prove it. So in addition to fulfilling basic fly fishing needs, rod companies provide offerings for just about any specialized fly fishing application you can imagine. And some that you can't.
It is truly amazing to me. American affluence and credit created the environment for an industry to supply the Golden Age of fly fishing tackle. There now are almost no bad fly rods made because the competition drives the dregs into almost immediate obscurity. All this, by the way, is also why there is some other angler standing on a rock wherever on the planet you want to go fish in relative solitude for some restful alone time.
But now, as always, as anglers acquire more experience and more fly fishing interests, they acquire more fly rods in more lengths and line weights. And the rod companies thank us all for that.