A rising tide lifts all boats. The demand for industrial diamonds is insatiable. And for bigger grits. This leads to people learning how to make bigger and stronger diamonds. Eventually some of the knowledge and tech will percolate to the jewelry side.

So simply, produced over time by a different kind of intense heat and pressure.

It depends what you use it for. Abrasives can use pretty much any horrible misshapen brown rock of roughly the right size.

But there are also applications for larger flawless crystals in things like diamond windows, semiconductor substrate and microtomes. Recently you can even buy a diamond 3D printer nozzle for extruding abrasive materials like carbon fibre. These require better processes than the ones that churn out abrasive diamonds.