I wouldn't say it's that stable or that the rest of Africa is instable, especially compared to Europe. It's just that Europe industrialized earlier and got to reap rewards that can only come from most simple needs being met easily.
In general, the developing countries are mostly "behind the curve", meaning their economic growth mostly wasn't that much lower for most of history, but rather they started somewhat later, often because they needed the technology developed in the west (modern agriculture mostly) to start increasing their population density. As far as I understand it, Africa is suitable for both very primitive and very advanced agriculture, but not much "in between" and so they got stuck with hunting/gathering and subsistence farming. They also didn't have access to proper domestic animals before Europe industrialized, though they had better animals than the South Americans, apparently. Neither a LLama nor a zebra can pull a plow.
Many countries in Africa were jumpstarted by colonization, and the colonists didn't have any interest in making that growth sustainable or giving the natives the tools to sustain that growth on their own. That's why white African farmers can say the black Africans can't manage huge farms for sh. Well, the white farmers didn't teach it to them and prevented them from learning it on their own...
Ethiopia is probably slightly different.