[1]: https://www.nasa.gov/sites/default/files/atoms/files/public_...
One of the purposes of using the "right rated" parts is that you get to off-load some of the testing and screening that you might otherwise wish to do to a component vendor (who is better equipped to absorb the price of testing, and because they have tighter integration with manufacturing, a better ability to achieve specifications).
Like I totally get the idea of using lower cost components. But sometimes they are actually the solution. And sometimes finding the problem is incredibly expensive, if not in $$$, then at least in PR.
Americans love to shit on gold plating, but they also love to shit on greedy corporations minimizing the bottom line.
The issue here (as a sibling post points out) is QA.
The problem SpaceX had was using industrial grade parts when they should have used aerospace grade parts.
I was looking at the details of the problem, and suggesting that those parts were neither aerospace grade nor industrial grade, but something lower still.
Non-rigorous testing is a reasonable thing for "industrial grade". I am not convinced that being far under half of the rated strength is a reasonable thing for "industrial grade".