That is not the reason, of course, it is just party-line parroting of the anti-gun activists. Pizza Hut is a division of deplorably named Yum! Brands, Inc. whose management, like that of all publicly traded companies, must act in the best interests of its shareholders. One effective means accomplishing that is avoiding needless lawsuits. Allowing staffers to pack heat, even while making deliveries to dirt-bags in dirt-bag neighborhoods, is a surefire way exposing the company to lawsuits from survivors of those shot dead by employees defending themselves during a stickup ("He was a good kid, just beginning to turn his life around--somebody's gotta pay!, " those grieving survivors, their lawyers standing next to them, will angrily sob to the TV reporters).
Given the litigious climate in this country, credulous juries and the unchecked propensities of shameless, ambulance-chasing tort lawyers to play the legal lottery, it is probably in a company's best interests to risk the tragedy of the occasional murdered employee than to open itself up to ruinous lawsuits from those, or their heirs and assigns, who murder them.