Air Traffic Controller Discussion With a Global Perspective
By Arvid Hansson 1162891
#531515 Because the vast majority of people have to attend either work or school during the day.

The vast majority doesn't however include everyone. As of writing this it's still before noon in (most of) North America and there are currently two enroute positions as well as a handful of towers open, so saying there isn't any ATC online during the day is not entirely accurate.