> It's unclear why or how could a disequilibrium form and stand in a free to travel country: as long as the metropolis offers even a modicum of economic opportunity, such as being a water seller at the intersection, that is already much better then being a subsistence farmer in an overcrowded country that experienced famine as recently as last year.
Lagos and all of Nigeria suffers from the same plague that is consuming the West: extreme inequality. There's economic growth but when the rich capture the overwhelming majority of the new wealth then, combined with population growth, you can get a population where many people are actually worse off as time goes on. This is why even as the economy grows the number of people living in poverty is actually increasing [1][2].
It's highly unlikely the government will/can/wants to address the inequality [3]. At some point the only "fix" to this problem will be, as it has been in the past, war. The growing regional and ethnic divisions just need another decade or so (by that time we'll probably see as many as 120m living in poverty) and then, suddenly, the water reaches a boil.
Ironically, if you speak to many Nigerians they'll tell you that inequality isn't a problem at all. If you work hard and smart enough you can make it. Sound familiar?
[1] https://www.stearsng.com/article/inequality-in-nigeria-is-wo...
[2] https://qz.com/963465/some-of-the-worlds-biggest-countries-h...
[3] https://www.oxfam.org/en/even-it-nigeria/nigeria-extreme-ine...