Look at the age of the staff - they're students, paid a pittance and are working during a very busy period when everyone else is off enjoying themselves.
I was in Home Bargains today, there were very long queues at the open tills, and a lady in front of me very politely asked the till operator if they could open another till, after being ignored three times she finally got this reply spat back "there's two open till there"
"Sorry, that wasn't the question, can you open another till to clear the queues"
"No we can't"
Well, luckily she was quickly proven wrong when the manager noticed the queues were blocking most of the aisles and opened two more tills...