I think if you work for your money , you tend to be more careful about spending it.
I always thought of criminals as make money spend money types.
I've known a good amount of drug dealers who earn way more than the average worker but 90% of them have an expensive vice. Coke heads, hookers etc..

Also , nowadays a really rich crook has to be careful flaunting his wealth. It can easily be taken away from them. As many lcn guys know.