The magic ingredients were inexpensive microcontrollers, massively paralleled mosfet transistors (also a product of large scale integrated circuits, since they

The magic ingredients were inexpensive microcontrollers, massively paralleled mosfet transistors (also a product of large scale integrated circuits, since they are actually millions of tiny mosfets working together), and the expiration of several key patents that made it possible to have a commercial explosion around the reprap scene. The patents expiring was a big deal, since the main patent was on the fused deposition process itself. The other factor was that normal desktop computers had become powerful enough to run sophisticated 3d modeling programs and make machine motion computations from 3d design files.