It's the dumbest design ever - taking the part of the bike that functions more as a shock absorber than any other part, and making it out of a material with no endurance limit and with inherent manufacturing flaws. With continued use, they are guaranteed to crack at some point in time. Even forged aluminum with fewer and smaller inherent flaws, would eventually crack in this application.
The beauty of steel is that it has an endurance limit - a stress value below which it is monolithic and will not crack.
I'm a metallurgist and licensed professional engineer. Stated simply, I know more about destroying things than anyone else you may know. About 10% of my work is product liability litigation - 90% doing the same thing for industry.