That background is useful, though it seems more like "how" than "why" - my instinct is James C. Scott-style rebellious hinterlands[1] but I haven't gotten a sense if the bandits are the product of social dislocations, or just opportunists. My naive assumption would be all of the above, some conflicts along the edges of Sahel being ideological or about lack of resources or political participation, and others being just smash-and-grab (not that they're mutually exclusive).

1: https://en.wikipedia.org/wiki/James_C._Scott#The_Art_of_Not_...