Why must all metal enclosures of station equipment be grounded?

Grounding all metal enclosures is a fundamental safety practice designed to protect the operator from electric shock. If a component fails or a wire frays inside the radio, a high-voltage live wire could accidentally touch the inside of the metal case. If the chassis is properly grounded, the dangerous current will immediately flow directly to earth ground. This massive current draw will intentionally blow the fuse or trip the circuit breaker, instantly cutting off power. Without a ground connection, the metal chassis would sit there energized with hazardous voltages, waiting to shock the next person who touches it. Therefore, grounding doesn't prevent a fuse from blowing; it actively relies on blowing the fuse to eliminate the hazard.