Because Bush-appointed US Attorney Alex Acosta (until recently Trump’s Secretary of Labor) made an illegal plea agreement to let Epstein off the hook and cover up the details of his criminality. https://www.miamiherald.com/news/state/florida/article226577...
Some extremely rich and powerful men were among Epstein’s child-rapist co-conspirators, so there are strong pressures on law enforcement officials to sweep the whole thing under the rug.