There are also trends in the styles of guns folks like to build, and the way they build them.
In the 1970's and 1980's I noticed several trends happening. As I look back I think that books drive much of the work that is done. Kindig's "The Kentucky Rifle in it's Golden Age" drove recreations of Golden Age Pennsylvania longrifles for decades.
Saving lost skills: At Colonial Williamsburg and other sites, the art and mystery of recreating the longrifle using period techniques was recovered and saved for posterity. This was the theme of Foxfire books.
High art: In an offshoot or different direction, rifles were being made that resembled originals, but were finer in execution and artistry than all but a handful of originals. Bivins is a good example of a new school builder in my mind, who sought to improve on the originals while making them easier to assemble, so the art could be given more attention. By chance, certain styles (good choices) became the norm. The Lancaster is an example that became the norm in part because of Bivin's Bicentennial rifles. If he had chosen Reading rifles, or early York or even Maryland rifles, we might not see a million "Early Lancaster" and "Haines" rifles being made. I like 'em, but it's funny how trends occur.
New Schools Developing: At the same time guys like Herschel House were reclaiming the backwoods artistry of the Southern mountain rifle and developing their own new styles.
Scarce components: For the average maker in the 1970's and 1980s there were limited components and few if any longrifle or fowler kits as we know them now. Folks who wanted to make a Bucks County rifle, etc had to work from blanks. Many to most builds involved the making of some components, and those of us who teethed on William Buchele's book made simple triggers, all the thimbles, nosecaps, sideplates, sights, tenons, and patchboxes as a matter of course. Most barrels came unbreeched.
Mining the early vein: Many current builders were strongly influenced by the quest to find the earliest American Longrifles. There were pioneers there- Shumway of course with his documentation and publishing, Jack Haugh with his early Christians Spring rifles, Monte Mandarino dabbling there before moving on to Euro style stuff. The mining continues. Many are inspired when a new early rifle appears- like the Oerter Griffon gun, etc.
Re-emergence of the fowler: Grinsdale's book on fowlers is strengthening the wave of fowlers being made. This reflects the shooting for fun aspect of the sport, or building for art, because the fowlers offer new stylistic explorations. In the early days it was all about paper punching. Now some of us are old enough to shoot squirrels with birdshot.
That was rambling.