This quote comes up often in SJ biographies or anecdotes and they universally attribute it purely to aesthetic concerns. Admittedly the man cared quite a lot about "beauty", but I've always thought this was more about the caring and less about the beauty.

To spend time making something most people never see look just as good as the things they do see you have to care quite a lot. This care begets a wide range of (usually) desirable secondary effects brought about by diligence. In my view it's similar to the effect of spending the time to make many iterations of a thing versus one perfect thing, with the former usually resulting in an end product much closer to "perfect".

This can also be seen as a way to filter the customers. "We only care about customers who care about the visual quality of the board that nobody ever sees." In other words, customers who are driven by aesthetics, and who have the means to support the habit of buying extra quality things, maybe with a whiff of conspicuous consumption.

If anything, it's a good, high-margin market. Beside the actual piece, you sell both self-appreciation and status. Apple long tried to make their products closer to fashion accessories, with some success.

A real estate agent walked through my house I was putting for sale. He examined the switch plates carefully. I asked why. He replied that a good craftsman lined up the slots in the top screw and bottom screw, and this was a "tell" that he'd done a good job.