ELI5: why the U.S. Naval Academy puts the most astronauts in space?

This question is very much U.S.-centric. I understand that significant portion of NASA astronauts, and it was everyone in pre-SST era, come from fighter pilot background. Makes sense, the space flight requires aptitude similar to high-performance aircraft. Looking at the U.S. military arsenal, the U.S. Air Force has twice the number of of fighter jets than the U.S. Navy and U.S. Marines combined (1527 vs 790). Assuming that service academies are the main sources of those pilots, how come that the U.S. Naval Academy is the undergraduate institution that puts the most NASA astronauts in space?