I think - the employees are dealing with hundreds of customers each day, some of whom are rude, some of whom think the rules are ridiculous and don't follow them, some of whom just make a mistake and accidentally don't follow them.
If they are sometimes a little short, or don't have time to ascertain whether you are a dick who thinks the rules can 'get to fuck' (like some pp) or have made an honest mistake, who cares?
They turned up to work and did extra shifts when everyone else was safely at home, when we didn't know much about the virus at all, when people were fighting over loo roll.
Who honestly cares if an employee asks you to stand behind the line or follow an arrow? Who is really so sensitive that this upsets them?
They're doing a difficult job in difficult circumstances. They haven't chosen to be there, they won't be walking out in half an hour with some shopping. They're worried, stressed, getting shit from managers if they don't enforce the rules.
The people I know who work in retail are not enjoying the power trip, as some seem to think, they just want to keep everyone safe, keep their job and go home.