Here’s an explanation from an article in The Guardian (UK):
“It was under British rule that Champs, a championship for the country’s top high school runners, was founded in 1910. It has developed into Jamaica’s biggest annual sporting event, attracting up to 2,000 athletes and daily sell-out crowds every year of 30,000. It is the tip of a competition pyramid that sees children across Jamaica start to take part in sprint races from the age of five. Wherever you find a piece of wasteland on the island you will inevitably see youngsters arranging impromptu races dreaming one day of making it to Champs…Every great Jamaican sprinter appears on the Champs honours list.
For decades the event was also a fertile hunting ground for United States universities who, armed with lucrative scholarships, lured the best teenagers. But they were often burnt out by coaches determined to get their money’s worth and so failed to fulfil their potential. The difference now is that if you are as talented as Bolt it is possible to stay on the island to train and travel to Europe to compete in the top meetings where you can easily earn more than a million dollars a year. By staying to work with their respective coaches, Glen Mills and Stephen Francis, Bolt and his compatriot, former world record holder Asafa Powell, have encouraged others to remain and that has helped raise the standard.”