Just given the nature of diamonds and light, there are more interesting shapes. They could cut it into a simple cubic, but that wouldn’t be very interesting and you would still have some substantial pieces left over to make other diamonds from. So the usual plan is to cut more or less the largest stone you can while avoiding any major flaws and using a cut that will display the properties of diamond in their best light, and then cutting the rest into diamonds that can be sold, as well. I believe there was a larger diamond found a while back that had two fairly large diamonds cut out of it because the nature of the uncut diamond made that more profitable and esthetically pleasing than if they had just cut a single larger piece.

Diamonds are interesting and can be pretty, but they’re also valued for vastly more than their worth, and there are other very interesting options for jewelry that are neither as expensive nor as ethically dubious as many diamonds are.