I go into muzzleloading in the late 80's, but only got into flintlocks a couple years ago and I think there's a few reasons...
Muzzleloaders in general don't get much public advertisment to speak of and when they do, inlines are typically shown;
Sidelocks are rarely advertised even in many general hunting magazines, and when they do, percussions are often shown;
Except for the occasional rare article on flintlocks, they mostly remain out of sight, and unless you know someone who has one to show you, an individual usually has to evolve to that point through his/her own interest, etc.
Right or wrong, heavy inline advertisement, and firearms companies jumping on the bandwagon to produce a variety of inlines, sends the signal that if you want to get into muzzleloading, the inline is the way to go;
And if someone does want to try sidelocks, a percussion sidelock does appear a little more straight forward to someone venturing into an area he/she already knows that they know very little about.
Plus there's the notion that newer must be better (must be easier) is driven into our minds even just watching movies...we learn to associate the flintlock way back during the Revolutionary War, and we learn that caplocks were used in the Civil War, almost 100 years later (100 years newer).
Given all the above, the "old", "rarely seen", "seldom advertised", strange looking contraption called a flintlock,
and incorrectly referred to as "flinch-locks", etc, don't get much of a fair treatment and can be intimidating, even at an unconcious level.
By contrast the reason Coca-Cola and Pepsi continue to be the dominate worldwide soft drinks is that they never stop advertsing about them...every day, every week, etc. If sidelocks, flintlocks, etc were advertised as heavily as inlines they would have a much larger following.
I started with an inline, then my overall interest in muzzleloading got peaked and I went backwards in technology to a percussion sidelock, then got away from sabot/bullets to patched round balls, then finally to flintlocks and real black powder...basically now all that I shoot
