we must recycle and be kind to Mother Earth ?
Nope. It all has to do with flight safety.
If I fire my gun and my wingman is behind me, his aircraft could ingest the casings into the intake.
Catastrophic for a single engine jet.
No good place to put the ejection port where the empties won’t cause problems. Remember, the F-16 is the plastic fantastic fighter. Also, the empties are used to help keep the plane’s weight and balance in line.