According to the statistics provided by your department, none of these murderers went on to kill again. Only 13 out of 127 committed offences that sent them back to prison.
You seem to be making an argument of the fact that, in a very large number of cases, if not the majority, the judge grants the application to use these provisions, if the individual is eligible to invoke the provisions. Now, you wish to make the test applied by judges more rigorous. If the test were as high as you say, it would not be surprising to have individuals whose applications were granted by judges receive unanimous approval from juries.