I agree with you about that, but these employees have chosen to do a job where they come face to face with customers daily, and some of those customers may get offended by seeing an employee wearing a BLM badge, in red states for example. The company doesn’t want to antagonise a potential customer and lose a sale, so they’re asking that no employees wear any political markings. And honestly, I think that’s a fair request if you work in a customer-facing role.
Notice that this ruling only applies to Whole Foods workers, not Amazon warehouse workers, who can probably wear whatever they want since they don’t deal with customers.