There is a reason to why we coop up at night and I thought of all people Ushijima would know. It's dangerous at night, now in the modern day now but at night things go hunting, it's harder to see at night so it's easier to die, and we're not nocturnal so we rest at night. It's instincts as Bokuto said. Biological instincts. We actually have a mechanism in our bodies that breaks down a certain chemical when it is dark and makes us sleepy, that's why artificial light messes with our sleep schedule.
