They are not "poorly industrialised", they are the other half of industrialisation. Think of the Rick and Morty episode where they split themselves into good halves and bad halves.

The industrialization of rich nations did not make Africa poor.

Once upon a time, everyone was poor. Then, some countries industrialized and others didn't. The ones that didn't are still poor today.

Some countries like China have recently pulled themselves out of poverty through industrialization. Someday Africa will do the same.