One reason that the bringing out of a guitar’s best voice is the main challenge for steel string guitar makers today is that there is no agreed-on standard to aim for. This is so for two reasons. First of all, most of the makers of this instrument have never heard a steel string guitar with a really great voice of its own. Therefore their idea of great sound is frequently based in hearsay instead of direct experience, combined with a lifelong experience of having conventionally overbuilt guitars as their models. It is understandable that they’d knowingly or unknowingly copy these models – which, despite the fact that their own guitars might look distinctive, they are really copies of copies of copies of copies of copies of copies of the same essential concept/blueprint – in the belief that their job is done when such an instrument is faithfully replicated and strung up. I say these things without intending to offend anyone, but because this is the territory as I see it.
The second reason is that whereas classic guitars are all pretty much the same size and shape, steel string guitars come in a wide variety of shape, size, and depth. This complicates the acoustic part of the work. It does so in the same way that a marksman is always called on to do the same work in shooting, but his emphasis will vary slightly as his various targets are placed at different distances away. Same skills, somewhat different factors.
Classical guitar makers, in my opinion, have more of a clue as to the sounds that better guitars are capable of: they have more of an agreed-on standard for what the Holy Grail of sound is (it is largely thought of as having the power, clarity, projection, and otherwise operatic voice that one would expect from a concert guitar). They also have had access to musicians with better-trained ears and better guitars, as well as other examples of more optimally-realized modern and historical models to study, listen to, and emulate. In comparison, the most familiar and widely accepted steel string guitar is the one that you can always plug into an amp or play into a microphone.
What I said above about “getting the most out of a steel string guitar’s potential” probably sounds too simplified and vague to be very useful. But consider the matter in this way: an OM model guitar and a Dreadnought differ in a number of specific ways: woods, scale lengths, body depth, possibly stringing, etc. How is one to factor these differences in? The best thing that a luthier can do is to make a really good OM and/or a really good Dreadnought; each will have its own voice because it will have brought different things to the table, blueprint-wise and tone-wise, from the very beginning. To repeat what I said above, the guitar maker’s task is to bring those qualities fully out without overbuilding, underbuilding, or misbuilding. And in the case of guitar makers just as much as with marksmen and cooks, it takes time and experience to learn to do the work professionally and well.