There are many reasons why people are late for work, and the most common reason for being late is sleeping in. Coming home after work can be stressful and tiring, but most people have other things to do. Foresay: eat, make food for kids, finish projects, etc. Therefore people go to be late, and the wake up late. About 50% of workers that go to sleep on time, wake up early and get to work on time. Then 50% of workers that don't get to sleep, wake up late and get to work late.
Coming in late is actually more common then you think, it happens everyday to millions of workers.