I think scientists are starting to discover this is more common than previously realized, though really it is pretty self-evident. Someone, long ago, finds a tree, bush, or other fruiting plant that has really good fruit, better than he or she has ever tasted from that species. That person takes the seeds or cuttings from that plant to propagate. Seedlings, cutting-grown, and/or grafted plants begin to be spread around. Since this new fruiting plant is better than the old fruiting plants, those old plants are not grown anymore or only grown in very small quantities. After a while, all the plants grown of that particular species are descended from that single, original plant. That is fine, until some pest or disease inevitably discovers that we have created a genetic monoculture of plants very susceptible to pests and diseases.
The process is ongoing as we speak. After all, one can only look a few decades into the future and extrapolate how Zill-developed varieties are likely to become the dominant ones for mangos, sapodillas, Surinam cherries, etc.