time. because of developed technology that is pervasive in our modern american lives we simply have more time to spend on doing the things we WANT to do rather than the things we HAVE to do. even our modern tools, for the most part, simple let us use our time more efficiently. we can accomplish more with less effort.
I think too, that we are working for for a different customer base, either for our own enjoyment, "On spec" or for customers who know they are buying a work of functional art. In any case, for the most part we have more time to put into a project; though our full-time and professional builder may dispute this factor. I suspect that for many of the original era builders production time and rates were much more of a life-or-death issue, economically for the builder and literally perhaps for a customer.
Improved health, (Including eye care) When I think back to my grandfather's aching crabbed up hands as he tried to work, in his farm workshop when I was a little kid, I give thanks regularly for advances in medical care. Imagine the working environment in a 18th century workshop, light levels, air filled with dirt, dust, and smoke on regular intervals. It not only impacted the actual working conditions but the workers health and ability to work as well.
To reiterate, the internet and modern communications in general. Also the regional associations, both formal and informal as well as shows and trade related fairs, as ease and ability of travel, even the now archaic telephone and modern mail system. All of these foster an active and vibrant association of builders spread over states, nations, and even continents. In the earlier era you might have has some local association of local regional builders and of course the master/apprentice relationships; but nothing like we have today. there is probably much more along these lines if we stop and think about it.
One could easily argue that NOW is the Golden Age of the American Long Rifle