Kama hii akili yako ndio Kila manzania ako nayo then Tanganyika has a long way to go.
Who told you that everybody is supposed to be poor in a country just because their country is ranked as poor? Do you know a thing or two about scientific data? How it's collected and sampled?
Just because those countries are listed as lower income countries doesn't mean you can't get one or two rich people in them. It's about the majority, not one or two rich people. Even America has poor people, just in case you didn't know. Not everyone in America is rich, just the same way not every single person is Tanzania is poor.
The difference is, majority of Americans are rich while the majority of Tanzanians are poor.