The report is very exhaustive and does offer an answer to the 'why', albeit not to the satisfaction of most armchair investigators' curiosity: 'We can't know with a high degree of certainty'.
Through comprehensive examination of all the available evidence, several plausible contributing factors have been determined and explored in detail, leading to several safety recommendations in an effort to learn from the errors made and prevent reccurance, but there is no smoking gun and nor are we likely to ever find one.
IMHO