1 They are suffering from insomnia
Some people may have insomnia or other problems that restrain them from falling asleep. The problems they are undergoing will keep them awake for a more extended period while they are in bed, making them sleep late. Due to which they wake up late the next morning.
2 They have a phase delay
Phase delay is the time delay of the phase as opposed to the time delay of the amplitude envelope. People who practice it might wake up late as they have changed their biological clock in a way that their bodily rhythms are not aligned with their daily schedule.
3 They are insensitive to ambient sounds
Some people's sleep is very sensitive. Even if they hear a very light noise or ambient sound from a background, their sleep gets disrupted, and they are enforced to wake up.
4 They need to sleep more
Some people need more time to sleep than others. For instance, a person can feel fresh after having a sound sleep for 5 hours a day, while the other person may still feel sleepy after having a sound sleep for 7 hours. Hence, people who are aware of their more extended sleeping patterns, usually sleep early. Otherwise, it will be hard for them to wake up in the morning, timely. (See How to Have a Good Night Sleep?)
5 They do not sleep early
People who sleep late are the ones who find it hard to wake up early in the morning. The reason is that those people did not get adequate sleep required for their body, making them feel deteriorated to wake up early. If they keep on continuing this and make this a habit of sleeping late in the night, they may find it very difficult to wake up early.
6 They do not get enough sunlight
It might be very likely for a person to wake up late who is sleeping in a dark room where sunlight lacks. It is because sunlight enormously affects the human biological clock and helps the person wake up on time.
7 They do not have a fixed schedule
Different people might have distinctive reasons to wake up late in the morning. Some may be struggling to build up their career and did not get a chance to sleep on time; some people may be doing a party, because of which they slept late at night. The major problems arise when people do not have a fixed waking up routine. (See Why do I feel bad when I wake up?)
8 They have night owl genes
According to a survey, it was found that there is a 15 genes combination that is required for a person who would like to wake up early in the morning and sleep timely at night. However, if a person lacks any of the genes, they may not be a morning person and would like to wake up till late at night.