I would expect the repetition generally comes out of necessity. If he's selling the parts to feed himself or his family he's that much less likely to choose to stop if it means giving up some source of income, however ill-gotten.
It's more likely from "I got away with it, I'll get away with it again" - but I've not done deep research into thefts, but the ones I know were along the lines of "I need more money for more drugs, this will get me some money".
Had he struck once or twice and then left the rest alone nobody may ever have figured it out.