I did not know that. It still makes no sense too me.
I think it depends to some extent upon whether the jurisdiction in question has a determinate or indeterminate sentencing system. Under Minnesota’s determinate sentencing system, the offender must serve 2/3 of the announced sentence, without exception. Many jurisdictions pronounce an “indeterminate” sentence which usually sounds exceedingly tough, but then the parole/pardons board has the authority to consider parole long before expiration of the pronounced sentence.
It is difficult to make comparisons between jurisdictions with different sentencing formulations.