Their motivation for denying his release went like this: 

"The panel notes your prison record of good conduct, program achievements, educational accomplishments, positive presentation remorse, risk and needs assessment, letters of support, significant opposition to your release and all other statutory factors were considered.”

“However, parole shall not be granted for good conduct and program completions alone.  Therefore, despite your positive efforts while incarcerated, your release at this time would greatly undermine respect for the law and tend to trivialize the tragic loss of life which you caused as a result of this heinous, unprovoked, violent, cold and calculated crime.” 

It's like they're saying "You've improved greatly, done a lot right since the last time - but fuck you, you killed John Lennon!"

However, Iike people before me have said, it's probably for his benefit that he gets to stay in prison. I'll imagine it to be a whole lot of people who want him dead if they release him!