I'm going to take a guess and say it's because of ruby lasers. They make massive synthetic ruby rods for lasers, but it needs to be one solid piece with very lo

I'm going to take a guess and say it's because of ruby lasers. They make massive synthetic ruby rods for lasers, but it needs to be one solid piece with very low impurities. A small defect will cause the rod to be entirely unusable for a laser, but there can still be large portions usable for other purposes with less stringent requirements. An example is ruby tipped 3D printer nozzles, used for abrasive filaments, which can be had for around $50.