They pay a lot more than the average retailer, which is why they feel they can work their employees so hard. I think they also tend to see less employee on employee violence.
Shared hatred of <outgroup> leads to increased cohesion among <ingroup>. Tale as old as human civilization. Maybe one day we'll be able to hack this quirk of humanity on a large scale without needing <vulnurable marginalized population> to be the artificial outgroup.
One I've seen that I think might have promise is "white people" being the outgroup for "white people." Any collection of white people forms an ad hoc in group where some nondescript "everyone else" is the outgroup. Now everyone has a shared thing to hate but everyone you interact with becomes temporally part of your ingroup so you're never hating an specific person or group of people. And even though it's impossible to actually become part of the outgroup you still have some of the fear that if you embody the negative traits that are ascribed to the outgroup you might join them so it also gradually norms.
More that employees who show up to work drunk or high can be easily fired and replaced, while more normal warehouses usually start the shift with people who just don't show up and are stretched enough as it is.
