But that just makes it seem discriminatory and unbalanced so apparently some managers want the theatrics 24/7 to avoid the complaints of unfair treatment.
This was in the back of my mind the entire time I was reading your comment. They may want to stop shoppers based only on when they see red-flag items in their cart, but that would leave things open for the door hosts to (consciously or not) stop shoppers based on the appearance of the shopper themselves. To mitigate that gray area, they decide to just stop everybody.
YOU GET INTO INTERNET ARGUMENTS ALL THE TIME, YOU FUNGDARK! YOU'RE IN ONE NOW!