Earlier quoted context omitted.
Because it turns out you actually can 3D print some of these in mass quantities. Some of the printers we are working with right now are producing on the order of 10s of thousands of parts per day. And now, there are tool shops in the US right now cutting injection molds to make those parts in the hundreds of thousands of parts per day.
The kind of 3d printing Prusa does (and provided plans for) is a tabletop/ amateur printer, not something which can scale.
So no, they do mass-produce with them: https://youtu.be/BjoQw5fGk6Q