Actually, the economics didn't work out to favor discrimination. The change was not as slow as many people liked, of course, but the change was there. Where discrimination was really entrenched and difficult to change was in government. It was racist government policies that really kept segments of the population down, and in fact, many of those racist policies still exist today. For instance, the primary motivators of the anti-drug and anti-gun laws were racist. "Saturday night specials" were regulated because they were popular among poor blacks for self defense. The sawed off shotgun, which is actually safer (because the shorter barrel means wider shot spread and makes the firearm less lethal) ware popular among italians who wanted protection from the mob, so the mob leaned on white politicians and got them banned, good for the mob, and served white political ambitions, etc.

Where there has been no supply (the small country example) blacks, for instance, often would band together and form businesses that served their community. This was inhibited by government regulations that would often deny them the "license" needed to operate that business... but it was not economics that kept those businesses from forming, it was regulation. (And where there wasn't regulation, the businesses would form.)