@acura No pardon necessary, you aren't "ignorant" ignorance is a result of ignoring information, you have inquired and it is my duty to explain what and why.
First, YES I am a Paramedic and I earn my living working on a regular ambulance just as you say, in a vehicle provided by my employer. I do, however, volunteer my services as a firefighter and paramedic when I am off duty. The area where I live is remote and any medical response can take 30 minutes or more because these ambulances are so far away. So I have purchased medical equipment and a response vehicle to fill in that gap.
Second, Because of the distances and the large area that we serve it is a much better use of resources to get volunteer "A" to go get the apparatus while volunteer "B" quickly makes their way to the scene. Otherwise a response would be delayed while "A" waited on "B" to get to the station to respond.
Third, In the US there are laws that govern emergency response and especially private citizens using emergency warning devices. Some places it is OK, others it is forbidden. Ironicly, where I work it is forbidden and where I live it is actually encouraged. BUT Emergency vehicle operators must take and pass Emergency Vehicle Operations Courses every year.
Lastly, Some locations use an intercept program where all ambulances are Basic Life Support. If an Advanced Life Support response is necessary (heart attack, asthma etc) the ambulance responds and the paramedic intercepts the crew in what is commonly called a "Fly Car". New York uses this system extensively because it is cost effective.
So there you have it in a nutshell, Some services have a paramedic on every truck and plenty to go around. Other services have only a few paramedics so they spread them around, and our little community has an ambulance comming from a long way off and just a handful of volunteers to keep the patient alive until it gets there.
Our customs and laws may be a bit different but we arrive at the same conclusion: use the resources that you have to save as many lives as you can.
The other side of the coin: I love to chase storms and reporting severe weather to the local Skywarn nets and the National Weather Service and that means more radios! BUT I do NOT use emergency lights and sirens to chase storms, that would be illegal.