That's the point. He doesn't have to. He just says, "Dad, this bit broke. Can you redo it?"

The commercial product has to be fully licensed and tested to the n-th degree, which greatly adds to the cost.

Got it, I misinterpreted it, and humbly retract my statement.

S/he is pointing out that part of the reason mainline prosthetics are so expensive is because of the legal and regulatory costs that come with getting them approved for market.