A modern day mystery

Nicolette, from the Netherlands, has clearly spent too many hours in a row awake - and perhaps some of them at a nearby convenience store - because she asks

Why do shops that are open 24/7 have locks on the doors?

I know that some do not! My stepdaughter, early in her retail career, was a manager at just such a store; when the power cut out in the middle of the night, she had to trudge to the store and sit there in the dark waiting for the power to be restored because there was no way for the staff to lock the door and go home.