It was necessary due to Fleet users not wanting to pay for a lot of the items that the police package cars came with. Since the vast majority of Fleet cars went to taxi companies that service big cities, there wasn't a lot of concern about high-speed operations. They generally aren't pursuing anyone, so they don't need all the coolers, aluminum driveshafts, extra-large brakes, calibrated speedos, etc. They just wanted a solid base-model CV that they could modify as they needed for their unique application.
Since the taxpayers pay for the police cars, they can be equipped out the ying-yang and the agency buyers don't care. Companies have to turn a profit, so they're a little more selective about what they are buying. So Ford took the base CV sedan, put in heavy-duty cooling, electrical, and suspension components, and the P-72 was born.