I doubt that only one factor was at play here. Poorly mitered tubes that don't contact each other and also don't fully engage the Bb sockets are a biggie. But I'll also suggest that this BB was way over heated during brazing and I bet let to cool off real fast. Both weakening and embrittling the shell some. Then there's the rider's contribution. With such obvious evidence of poor drivetrain management (the chain sawed through ft der cage and damaged chainstay...) this bike likely had a rough life right from the beginning. Andy