Licensing because you use a channel and share the air waves. The FCC prefers everyone know what there doing instead of just pickup a radio and tell people get out of my way. Licensing goes further if you have a construction site of a good size and want to use radios, so your not interfering with Emergency responders and anyone else that may want to use the channel. Walkie talkies are fine but very limited range and only broadcast 1-4 watts typical.. A good truck mounted unit is 25 to 50 watts and more.. Out in the boon docks people do not install Cell towers so cellular phones are worthless without them. A truck mounted unit can be setup to work with job site radios but you have to make sure your on the correct frequency to communicate..
Most truck mounted units are good for 1-50 miles in range depending on Antenna, terrain, cloud cover, weather.. But think about the recent Carson 500 20 trucks all leave the same location two minutes apart. Figure traveling at just 30 miles per hour your going to have a distance of (30mph= 1/2 mile per minute times 40 minutes) 20 miles from the first truck to last.. If everything is exact.. Handhelds are going to work 1-2 miles.. There are several articles here with different radios and places to purchase. I have not heard one person ever say "dam why did I buy a truck mounted radio, should have bought the handheld"... Many people buy both and are happy to have them on the trail...