A small isolated shop might not want to order in the proper materials if they had what they thought was suitable material on hand. Small quantities of the appropriate materials are expensive and a small shop might not have the financial resources to acquire the materials unless the boat owner put money up front. Even if they had or could get the right materials they might not have had an experienced welder/machinist who could build the post armature at an appropriate standard. Independent of the rudder, looking at the CS36 drawings that are available on line, it looks like losing a rudder would damage the lower bearing housing and likely the hull penetration. Some glass skill and maching ability would be required to properly rebuild those boat parts. Finally, a typical boat owner likely wouldn't know the details of rudder fabrication and couldn't properly assess the quality of the build. All of those factors were likely part of the failure scenario.

On the other hand, in some places that rudder replacement would be a snap. I know that the three man shop I have been spending my afternoons at for the last few months could build a new rudder for that boat (or any other boat) at an appropriate standard. It might take 3-4 weeks depending on how long it took the metal fabricator we sub stainless work out to to acquire materials and make the post/armature up. I imagine the rudder replacement would cost over $5K though and it might be quite a bit more depending on how much work had to be done to the boat itself. There are several other local boat shops that could do the work at a world class standard, but they would cost more