Ken - its the "food chain" principle.
If needed, and if properly administered, a pond fertilization program will promote phytoplankton; which serves as food for zooplankton; which feeds other aquatic invertebrates (and some minnow/shad species); which feed your larger forage fish - such as bluegill; which feed your predator species. Basically, is is cheaper and more efficient to fertilize the low-end of the food chain than to directly feed the top-end predators.