Dutch national here. I'm pretty sure this is largely due to lenient prison sentences, no prison sentences at all for minor offences, and unsolved crimes. The cold-blooded convicted killer of the frontrunner in the Dutch elections in 2002 was released after 12 years, something which is unthinkable in other countries.
The main thing is that there's a difference in perspective. In e.g. the US legal system, prison time is punishment, a form of vengeance, of paying your debt to society. (and nowadays, a means to get a large slave labor force). In NL and Finland and the like, prison is more like forced rehabilitation - it recognises that committing crimes have a reason, and by solving the reason you solve the criminal behaviour.
As a Dutch guy, I agree with this in general. However, what the system does not take into account is that some people are just broken beyond any hope of ever being fixed. For example, there was a news story a while back about some petty criminal who stole some iPhones from a locker room and got caught. It was the 163rd time he got arrested. How do you deal with someone like that in a civilised manner ?