It isn't even just about a product the U.S relies upon. Noam Chomsky has explained this quite well. It's about successful defiance. If Nicaragua rebels from U.S imperial control, then even though Nicaragua itself isn't that important to the U.S, even though the U.S isn't gonna collapse if it loses control of Nicaragua, the example of successful defiance could inspire people in Costa Rica, Panama, Honduras, El Salvador, Guatemala, Belize, Mexico, and beyond into the Caribbean and South America. It's the example. Kissinger called it a "virus" that could spread. That's why the U.S so viciously, so brutally punishes anyone, anyone, who dares to step out of line. Vietnam, Cuba, Nicaragua, North Korea. It isn't so much about these countries themselves, but about the example they could set, of successful defiance, and worse, of an alternative mode of development, which if it inspires enough people, could eventually threaten American imperialist control over the entire world, and the capitalist system itself.
Just in case you misunderstand this post, i'm not justifying U.S imperialism; merely explaining it. I'm as anti-imperialist a person as you're ever likely to meet.