Sure, well lot of people just love shooting, but that damn noise.....oh man.
Second it is a matter of security and communication, its not a qeustion of making shooting totally silent as it practically is impossible, but more the relaxed feeling when shooting silenced, and be able to receive commands without being in doubt of whats actually has been said.
Example:
Hold fire!
Yes yes i am firing away.
Result: 20 dead children in a kindergarten