Public Works refuses to budge on full-scale "pre-emption" (always green), reserving that for emergency vehicles (who, coincidentally, don't use the systems PW has installed for them anyway, preferring to blow through intersections without signal changes).
People are used to stopping until they pass by, unless they’re blocking the vehicle and then they move.
Changing the signal to green wouldn’t change this. People are used to ambulances driving against traffic along side them and will wait at the light until it passes.
I’ve seen entire light cycles pass from red back to red waiting for a series of 3-4 emergency vehicles.