I get the sense that's happening more for show: businesses want people to feel safe coming in; bragging about thorough cleaning procedures is a way of conveying that, whether it works or not
Shouldn't store B then be spending less money on "sanitary theatre" and can theoretically provide a marginally better service in ways that matter?
The federal government can spend however many billions of dollars for new TSA staffing and equipment, but that's because they're a monopoly in airline security. Not sure why in a free-market we'd have obviously sub-optimal outcomes like this.
(Sorry if this is naive, feel free to weigh in with harsh realities about how the real world works :) )
I would even bet that most people issuing the cleaning guidance know that it is almost useless, but we live in a world in which it is more important for your actions to make you perceived the way you want rather than being effective.