I do like plain rifles where the architecture shines through without distraction. There are just darn few of them represented among the earliest colonial rifles (pre-Revolutionary War). And there are plenty of fancy ones represented in that cohort. If we choose to argue it's about survival and collectability, perhaps we should apply those same standards to later time periods.
I think sometimes we over-rate how much extra "fancy" would cost in the early period. There's a lot of work breeching and rifling a barrel, sawing a blank with a hand saw, inletting barrels by hand, roughing in a stock with hatchet, drawknife, plane and spokeshave, making many of the parts, and getting it all assembled together in a nice, shapely, finished package. Adding some moldings, some carving and a little engraving is no big deal for someone trained in those arts. Probably an afternoon's worth of work. I am not talking "A Verner-Gunsmith" style decoration here. More like RCA 52. That incised carving on the buttstock, a molding line here and there, and a little something around the tang, took maybe 45 minutes.
I do think I see quite a few plain guns made during the Revolutionary War period.