From the opinion:

In particular, despite the fact that 14% of California's misnamed "Lifer" population - which consists of over 30,000 inmates - are over 55 years old, defendants have taken no meaningful action to release elderly low-risk prisoners in this category.

Although defendants object to the release of elderly Lifers on the ground of public safety,it appears that 75% of these Lifers have been placed in CDCR's lowest risk category, and the historical recidivism rate of Lifers is approximately 1% - in comparison to California's overall recidivism rate of 48%. See Weisberg, Life in Limbo, at 16-17.

Moreover, elderly individuals are much less likely to recidivate as they are generally less likely to commit crimes. ("For most offenses - and in most societies - crime rates rise in the early teenage years, peak during the mid-to-late teens, and subsequently decline dramatically. Not only are most violent crimes committed by people under 30, but even the criminality that continues after that declines drastically after age 40 and even more so after age 50.").

It is more than likely that defendants could reduce the deficit with respect to the 137.5% population cap by approximately half, without risk to public safety, were it to make the appropriate assessments and take the appropriate actions with respect to these so-called "Lifers" alone.

I suspect Brown knows there is no way he will ever find the money to build more prison space, and letting 55 year old murderers go is not a winner either.

And, I believe Brown is opposed to the death penalty, so he is not a lock-em-up-and-throw-away the-key kinda guy.  

Perhaps the most important point was noted by Oculus--a lot of the low risk violent offenders have already been let loose early.....You would now be releasing inmates who were deemed too high a risk to let go last time....How close do you slice this issue of being a nonviolent offender?