I think in many places, lots of trails, even good ones, are based on previously established trail surfaces, as in BC (Before Cylists). Some of these have received attention, modification, work, etc. and over the years have evolved into good trails. To hack out a new trail by hand takes an immense amount of manpower, especially if it is to be of any significant length. This is one reason I think a lot of trail builders and organizations are taking the "quick route" by using machines, a byproduct of which is the relatively sanitized surface they produce. You gotta somehow leverage a lot of man-hours and planning to get some of those truly amazing handbuilt trails IME.