Very few poor households get loans from a proper lending institution like a commercial bank or a cooperative. Credit from informal soucers tend to be expensive. Yearly interest rates in the 40 to 200% range (or even higher) are the norm, and the poor pay more than the rich. Money lenders have a great risk, low default rates are anything but automatic, they require hard work on the lender´s part. Enforcing credit contracts is never easy. They protect themselves with high interests. Effort and time is what is taken away from the lender to receive the money back. To make matters worse, this creates what economists call a multiplier effect. When the interest rate goes up, the borrower has more reason to try to find a way not to repay the loan. That means the borrower needs to be monitored and screened more carefully, which adds to the cost of lending. This pushes the interest rate up even further, which necessitates more scrutiny and so on. This also explains why banks do not lend to the poor.
Social pressure. Discipline.
Finding ways to finance medium-scale enterprises is the next big challenge for finance in developing countries.