Why did/do Africans living in the heart of nature's drugstore, choose ineffective things like voodoo for cures?

Wouldn't it be smarter to explore the more effective solutions right in their own backyard? If the answer is, "well they don't have labs to test in", then why don't they? Before responding, please keep asking "Why don't they" until you discover a SENSIBLE reason why humans would allow themselves to be in such a pathetic situation.