I think one of the questions is whether microfinance works as a bank, to make a profit, or works in lieu of donations, where loans are subsidized and act as a force multiplier on donor money.
If I had my druthers, I'd set up a VC firm in the developing world, which funded businesses on reasonable terms, knowing I'd lose money, but:
1) Generating a stream of occasional successful enterprises.
2) Even for failures, giving people an opportunity to go through the learning experience of launching a startup.
That sounds like GiveDirectly.org with extra steps for the donors ego.
The US just gave $1200 to each of millions of Americans, all of whom have already income plus other govt benefits totalling high above median income in Nigeria. If you have money burning a hole in your pocket, why not give $1200 to a random Nigerian, average income $2500/yr?
Or even $200?
Mostly, because all that would do is cause is random inflation and inequity.
When donating money, you are reallocating resources. That can lead to improved economic growth, if for example you are allowing people to go to school, start businesses, or otherwise helping build such bridges.
More times than not, donations cause long-term harm. Look at oil in Nigeria to see how a massive simple influx of cash was not good for the population.
If you really want to help in Nigeria, you can help mentor a university student there. Your time will count for a lot more than your money. Or if you are willing to spend money too, hire a university student from there as an intern (likely remotely). That helps align a lot of incentives.
If I had my druthers, I'd set up a VC firm in the developing world, which funded businesses on reasonable terms, knowing I'd lose money, but:
1) Generating a stream of occasional successful enterprises.
2) Even for failures, giving people an opportunity to go through the learning experience of launching a startup.