I don't think that is a significant proportion of crime, though it certainly exists. Most crime is organized (theft, pickpocketing, robbery, kidnappings, drug trafficking, sex trafficking, racketeering), or it exists in an atmosphere of impunity, where there is a baseline assumption of no consequences (Epstein files, rape culture in certain industries).

But apparently there are far fewer such people in Singapore. How would you explain this?

I think the explanation is that growing up in an environment where even small infringements are consistently punished makes people think about the consequences more.