Why do government agencies spend so much money on polygraph tests if they aren't primarily used for prosecuting criminals?

Government agencies like the FBI, CIA, DOD, and other law enforcement entities spend over $50 million annually on polygraph tests primarily for internal vetting purposes rather than criminal prosecution. These tests are administered to potential employees as part of the hiring process. For instance, the FBI requires every job candidate to undergo a polygraph examination. Collectively, the FBI, CIA, and DEA process over 70,000 polygraph results from job applicants. This extensive use demonstrates that polygraphs are predominantly employed as screening tools for ensuring personnel reliability within sensitive government positions.