I guess we didn't get what was promised to us today. Maybe tomorrow
Here is a bit of history that points to why the busy tone was thought up in the first place. In the 70's and prior when LASD was on 39 mhzthe FCC only allowed emergency traffic repeated on VHF Low. When there was emergency traffic, then the repeater mode could be enabled. Not sure why it was carried over to the 480 other than for continuation of habit.
That also is why CHP did not go to repeated traffic until some time later when the FCC changed the rule
How I was told was because the way stations get picked up and dropped from the consoles along with similiar call signs from various stations it prevented confusion for field units, ie was that 173, 73, or 273 that needed assistance. Interesting of note is the directive about this upcoming trial asks us to start using our station along with the call sign when broadcasting. In other words, Norwalk 43k1 10-34 for a plate, or Temple 55 10-38 with 1. Instead of just the call sign. Well it is the Sheriff's Dept. so he gets what he wants.
Welcome to the 20th century, LASD... Yes, I said that correctly. I'd almost wager they don't keep it this way.