The island bet on multinational manufacturers, who bailed when the U.S. repealed a key tax incentive. Meanwhile, frustrated local entrepreneurs fled to the mainland. ARECIBO, Puerto Rico – Prudo Jimenez was born on a sugar farm here in 1941, when agriculture ruled Puerto Rico’s economy. He grew up to be a supervisor for drug maker Syntex in the 1960s, after U.S. manufacturers came in droves, seeking a tax haven. The peppy 75-year-old personifies an economic development movement designed to transform a generation from poor farmers to industry leaders. Yet when Jimenez started his own venture, a horse breeding operation, he couldn't make it work. His sons fared no better. Carlos Jimenez, 48, and Anjoe, 50, each started businesses only to see them go under in a decade-long economic slump that continues today. Families like the Jimenezes highlight the U.S. territory's failure over decades to nurture a sustainable economy, one anchored by local entrepreneurs,...