Also, I'm sure any crime that puts you in jail for longer periods of time have lower rates of reoffending, since you're in jail. Murderers also likely have low rates of reoffending.
Part of it has to do with why crimes are committed. Most sex offenders and murders are not serial rapists/killers, and as such only offend in very specific situations (such as killing a wife who was caught cheating). These situations are likely to not happen again. Compare this to other crimes which are more related to crimes of need. Joining a gang for the protection it offers (even if it doesn't actually offer protection, the individuals think it does) is not a situation that goes away. If anything during prison they become closer to the gang as they group up within prison to survive. Someone who was addicted to drugs is really likely to relapse into their addiction. Most individuals selling drugs have even less legal opportunities to earn money once they get out than before. And this isn't even getting into the class aspect of things. It isn't something that is really captured in a single paper but rather a larger topic.
It matters anyway. If you give someone a long prison sentence, their personality will be different when they get out. Crime is a youth phenomenon.