My completely outsider take on this is purely due to economic hardship. You see the same thing in poor neighborhoods, people turn to crime when they need to survive.
I don't think income may change people's probability to become criminals in a significant way. It will at most change the type of crime people commit.
Low income people tend to have low education and thus, when criminals, will practice "stupid crimes", like robbing people on the street or other things that look more violent.
Higher income people tend to have better education and so, when criminals, will go for more elaborate kinds of crime, like these hackers behind DDoS or those who steal credit cards. They don't look that violent, but I think the damage they cause to society may be even worse, and they are much harder to catch.