>The whole point of 3D printing is that the material is moldable when hot but rigid when it cools.

Which means what exactly? Aluminum will go soft under high temperatures as well, yet this part would not have failed if it was made out of aluminum.

The failure is not the material, the failure is someone neglecting the operating conditions or material properties when choosing materials.

This exact part could have also been milled out of some plastic and would have failed the same way. The method to produce that part is only relevant in so far it is open to more people.