I imagine that it was a combination of things.
As an apprentice you learned what your master taught you including the rules of thumb and layout techniques he practiced in his shop, whatever they were. The concept of a journeyman was to travel after you completed your apprenticeship and pick on new and different techniques from other masters for a few years before setting up as your own master. But a basic set of patterns had been engrained at the beginning. Some individuals are more flexible that others. They find it easier to adapt to new techniques and styles. I suspect that the older you get the more likely you are to stick to the "tried and true" as much as possible unless a new technique comes along that proves to be more profitable.
I think the other driving force I think is the market. People who's survival depends to any degree on a specific tool are real reluctant to make changes to what works. A gunsmith who built a good successful rifle, reliable, accurate, and well-priced for the local economy would establish a reputation among his customers and their associates in their region. His apprentices would naturally follow his successful pattern for the most part. A gunsmith moving into an area where there was a well established pattern would probably have an uphill struggle unless he conformed to the pattern to a significant extent. However a smith's reputation would also travel with him and an experienced smith of repute might well be able to introduce a "newer" style to more flexible and probably younger members of the community.
It is harder to factor in population and material culture movement patterns on the "moving frontier". I wonder how far behind the cutting edge the gun-producers lagged. Certainly the explorers and hunters on the edge had critical needs, but the nature of frontier settlement and warfare insured that even those well back of the edge had nearly as strong an need for arms of quality. farther back from the edge I suspect that established settlers could afford arms of a more artistic value. Then too there is the matter of male competitiveness and the desire to have a "better" gun than our peers
Another thing that has to be factored in somehow is how our perceptions may be skewed by the how and why of the available example base on which we are building those perceptions