wilbur
There are many reasons that I can think of as to why someone might go to the trouble of making a sandpaper cabinet to this degree of refinement.

1. Aesthetics. Maybe the woodworker just likes looking at a cabinet that isn't just shop grade plywood.

2. Class project. McKay did say that he made this with Chris Gochnour at Snow College. It could be that this size cabinet made as a part of a woodworking class wasn't a good size for the living area.

3. Prototype. Maybe this was a first pass prior to building the "real" project. If I was to incorporate all the different techniques that this project incorporates, since many of them are new to me, I would certainly want to do a practice run.

4. Wrong conclusion on the part of the questioner. The presumption is made that if you post about a project that you made for your shop, then people that post here "spend a larger fraction of their time making stuff for their shop than the folks that hang out on the other Forums." This is not a valid conclusion, as McKay's response above bears out.