There are many many factors that explain the success of a country. Some countries are blessed with a lack of ethnic divisions, a relative absence of ethnic strife. Some countries have wise leaders, and the Ivory Coast has enjoyed for the most part solid leadership. Some countries have reliable friends in the outside world, and both those countries do. Arms proliferation is a huge problem in Africa.
Governments there tend to be on the weak side and they are easily challenged by small armed groups.
We are not talking here about fancy aircraft carriers and main battle tanks. We are talking about AK-47s and mortars. The tragedy is that lots of middlemen are making a living by supplying arms to ambitious insurgent leaders, some of whom deserve to be called warlords, and making a good living doing it. There is certainly less concern about those minerals falling into the wrong hands. What's changed, though, is that there is no shortage of these materials, and as you know, commodity prices are going down.