Most Helpful Girl
Maybe they can't afford fancy clothes and it's a REALLY special occasion and they chose to go there. You don't know there story or reasoning you just have to mind ur own business because they only person you can control is yourself and you can either choose to waste energy on something you can't control that isn't important or you can't choose to focus on why you went to the restaurant in the first place wether it's your family, a date or just for food
Most Helpful Guy
It's one thing for the waiters/waitress do wear fancy clothings at a rich and luxurious place, but there's no rule for customer clothing, they're here for food, and food they will pay for.
Restaurant won't make money if they nit-pick on every single customer. It's not welcoming to be forced into wearing a style of clothing only to eat.
Point being :Let them wear whatever they want.