A cheap quartz movement (watch mechanism) will be more accurate than most high-end mechanical watches, and yet they keep being made. I think the main reasons (

A cheap quartz movement (watch mechanism) will be more accurate than most high-end mechanical watches, and yet they keep being made. I think the main reasons (beside "vanity") are: a) huge profit margins, limiting the incentive to optimize b) high start up costs combined with relatively little volume A system would have to accurately measure imperfections/inclusions, then pick the best design, then it'd either have to cut it themselves or communicate the instructions to the person (who'd have to be willing to use such a system). The current approach with a human designing and cutting the stone is simply good enough, so there is no reason to change. And something like re-cutting the Koh-i-noor happens rarely enough that I suspect nobody wants to invest in developing the software for it when you can get a close enough result by throwing more one-off manual work at the problem. Synthetic stones (which I assume are a much simpler problem because they're even cheaper and have fewer inclusions to optimize around) are already being cut by robots (or so I've been told, at least). I think the whole "real natural stone" and "hand-cut" parts are definitely part of the appeal/selling point. If you care about a "slam dunk", you'll buy robot-cut Cubic Zirconia or Moissanite and call it a day.