Why do loan sharks bother with lending at all?

Loan sharks often resort to harassment and violence to get debtors to pay up because they have legal recourse. If they can use violence, why do they bother with the loans in the first place? Why not just target innocent people for extortion (like the Black Hand and protection racketeers)? Is it the sense of obligation and the "if I just pay it off they’ll leave me alone" thought that makes the debtor more compliant?