Why some people stay up late?

Night owls are people who tend to stay up late even if there is no reason behind it. These people function better at night.

People who are loaded with work or studying tend to stay up late to finish what is required of them. 

Some people like staying up late to enjoy the calmness and quietness, as opposed to the loudness of the day.

Some people find working and studying at night better, as there are minimal distractions.

People who work night shifts, for example, are forced to stay up late, and even sometimes sleep during the day.

Some people find staying up late to be relaxing, as they are usually alone and have time to be with their own thoughts.

There are people who tend to stay up late out of sheer boredom and the lack of anything better to do. (See How does staying up late affect your health?)

People who are not restricted by curfews have the choice to come home late, and consequently sleep late.

Some people are incapable of sleeping early, which results in them staying up late until they feel sleepy. (See How to Have a Good Night Sleep?)

Some people have the habit of staying up late for no reason and find it hard to get rid of it. 

Some studies have suggested that people who stay up late are more intelligent than others who sleep early, due to a certain energy that they have.

Some people are forced to stay up late due to having certain commitments, such as tending to an ill person or taking care of a baby.