Imagine firefighters inside a burning building, just a few feet/meters/metres away from each other in the smoke, unable to communicate because a base station can't be reached through metal in the walls; police, perhaps in pursuit, whose comms keep dropping off network as they pass obstructions behind which no additional towers had been funded to permit coverage, and all this (as pointed out) where direct voice communication is not designed into the service. Could that be because it isn't billable? Hmm.
Nor do such devices have sufficient power to provide direct comms at the ranges ordinary analog transceivers do, the batteries being only large enough to reach a base station expected to be pretty much line-of-sight to the user and small enough to fit inside an almost matchbook-size enclosure.
Flames, because there there's smoke...