Why is it okay for some people to break the rules at work while other people get called on the carpet for doing the same thing?

I work in a chain store. You'd probably know it if you heard it. We have a dress code. The store provided polo, solid black, gray, navy, or khaki slacks. All black shoes. Your name tag has to be visible. A few weeks ago I got called in the back and told that my shoes, black gym shoes except for the Nike swoop weren't all black I could wear them until payday but after that he expected me to be in all black shoes. But all throught this time the head cashier who has been there for ever has been wearing black shoes with two white stripes and white soles. This same cashier also had on a hoodie at the register one day last week when the temperature got down below zero. I get that he was right by the door and it threw in a gust of air every time it opened, but it's like he can do whatever he wants and it's okay and I get hauled in the back about stupid spit. Okay if they are making an exception because of the cold, which makes sense, that doesn't explain why he can wear shoes that aren't all black. I'm looking for another job because I hate the double standard, so if your answer would have been love it or leave it, then you can save yourself the time and trouble.