There is a good book on this topic by Muhammad Yunnus - Banker to the Poor: Micro-Lending and the Battle Against World Poverty, https://www.amazon.com/Banker-Poor-Micro-Lending-Against-Pov....

Overall, it is difficult to be even stay in business let alone profitable due to structure of how interests work at that income level due to most not paying back on their loans.

I thought the point of Yunus's book/movement was that microloans were safe because people, on the whole, DID pay back the loans?

If I remember correctly it was set up in Bangladesh. You are correct people did pay back the loans but it required much higher interest rates e.g., 60%, due to small size of the loans and having to factor in those who wouldn't pay back.

My understanding is that Walmart and Amex's bluebird program tried to make things a little bit better, but probably doesn't address all the fundamental structural issues in place

Is it a "structural" issue? Or is it just the fact that, statistically, poor people are really unlikely to pay back loans, so loaning to them profitably means charging really high interest? Or is that a "structural" issue?

Bluebird (mentioned by the parent) is a checking account alternative (read: not a real, FDIC-insured bank account). No one's loaning anything in this case. It's designed to appeal to people who, for one reason or another, cannot afford to open even a basic traditional checking account.

Edit: Before such ersatz-bank-account services proliferated, I believe it was common for poor people to cash their paychecks at a check cashing place (which costs time and money).

The profit model is to fleece the most reliable customers.

This was covered in a recent episode of the a16z podcast: https://a16z.com/2017/12/24/democratizing-fintech-summit-201...