Is it because of the awkward territorial boundaries? Is it because of the power structures that were set up under colonialism? Is it because the first world wants to exploit them, and deliberately keeps them disorganized so they can't stand up for themselves? Is it because they entered the industrial revolution so late in the game?
I'm curious what makes old cultures so resistant to modern education. Do you think it's just vanity? (Don't want to have to admit someone else discovered it first.) Is it because it conflicts with their superstitions? (Maybe the reason Europe managed to keep its superstitions is because European education generally avoided conflicting with them when it didn't need to.) Is it because they vainly hope that modern technology will just go away and leave them alone? (Until their kids start wanting to drive cars.)
Now, I know a few countries, like Botswana, are not doing too poorly these days. You don't hear as much about the success stories, I guess, and I don't think we should count South Africa, since its (surviving) culture is basically European in origin, and always has been (at least since it became the country of South Africa.)