To give people a better idea of what we are talking about - here is a map of the fire stations in Mariposa County -
CA - Mariposa County - Google My Maps - the red markers are the Cal Fire stations - the blue markers are the county stations - the county stations are staffed by pager equipped paid on call firefighters - the Cal Fire stations are equipped with 1 or 2 pumpers each with crews of 3 or 4 in the station 24/7 in the summer - (lets assume it is summer)
Cal Fire typically responds to all calls near their stations - structural, wildfire, EMS, motor vehicle wrecks, wilderness rescue, etc. Keep in mind that many of the county stations have 6 or less paid on call firefighters. And they are located in very rural areas with very low population densities. Its not hard to see that Cal Fire engines will beat county engines to huge areas of the county - and by a long shot. Therefore the CalFire engines will often be the first responders and operate alone for 10 minutes or more until a county unit arrives.
Note - a typical structure fire response might get 1 or 2 CalFire engines plus 3 or 4 county engines and tankers, plus a Battalion Chief from 25 miles away. Plus aircraft, dozers, and handcrews if it is not a rainy day.
Note - a typical EMS response gets 1 CalFire engine plus 1 call company plus 1 county ambulance.
If a CalFire engine arrives at a mobile home fire, they have only 3 people to use. Lets say they have gone down a 200 foot driveway, pulled off a hoseline, and take it 200 feet to the front door. They look in the front door and see 3 victims on the floor. Their portable radios cannot reach the dispatcher from this location. They need to immediately call for 3 medevac helos or paramedic ambulances. What to do? Send someone back to engine and use the mobile radio to reach the dispatcher? You just cut your rescue force by 33%. Do you really want to do that at this critical point?
If a CalFire engine is sent to a report of a "motor vehicle off the road - unknown injuries", they will arrive on scene and walk thru the vegetation to reach the motor vehicle. If they find a couple of unconscious people, they need to radio for Jaws of Life and helos and such. But their portable radios wont work. They have to send 1 person back to the engine. Again cutting the rescue crew by 33%.
If a CalFire engine is sent to a "smoke check" and they are searching around thru the brush for a good access point, and they stumble over a grow operation with 2 guys with big rifles - who are they going to call on their radios? No one. Because they responded alone - they are operating alone - and they wont be talking to anyone until they hike back to the engine. BECAUSE THEIR PORTABLE RADIOS WONT WORK.