That's asinine. It's like saying "If brakes really mattered, a cop would check your brakes before letting you drive to work in the morning". Brakes are pretty damn important, but very few places (in the US at least) have any mechanism for ensuring yours are in working order even periodically.
Proper risk mitigation takes into account (at minimum) the likelihood of an event occuring, the severity of the event occurring, your willingness to tolerate a failure, and the cost associated with implementing corrections.
Airlines have an EXTREMELY low tolerance for any kind of risk that could conceivably lead to a catastrophic failure, so the fact that you're allowed to have a device, despite potential safety concerns, comes from a combination of a few factors:
The chances of some kind of major interference with flight ops happening are demonstrably pretty low
People would likely push back quite hard on not being able to use electronic devices for entertainment on a flight.
Most people comply with the request.
Related to 3, there is little reason for airlines to change the rule, since cell operation is next to impossible in flight anyways, and wifi/bluetooth are not in the frequency range of concern.