Hardware engineering is hard. Especially for any safety critical component.

In this case engineering was done by someone, who either did not understand the material he was working with, or the operating conditions in which that part was deployed.

Obviously no testing or any kind of proper engineering was done to create requirements validate them and verify them.

Being able to design a 3D model and print it does not mean you are done with engineering. It is just one step in a very long chain, which is needed to produce devices which stand up to their use.