Why do people with depression sleep alot?

Not sure. Major depression disrupts many body functions, including sleep and appetite--but it can affect both in either direction. Some people sleep much more, others much less; some have no appetite and lose lots of weight, others overeat and gain weight. Exactly why presentation can vary so much among people remains an area of intense interest.
Depression. Sleeping and isolation can be and "escape", for those depressed. These can forgo more serious problems and help should be seeked.
Exhaustion. Fatigue, exhaustion, low energy levels, psychomotor retardation are all "vegetative" symptoms of depression and indicate a general slowing of all activity. More sleep is the result. Also lower motivation and drive contribute to "wanting" to sleep all the time.

Related Questions

Why do people with depression sleep alot?

Not always true . . Depression can alter sleep patterns, as can stress, diet, anxiety, alcohol, work, medications & lack of exercise. Depression can result in changes in neurotransmitters such as serotonin, Dopamine & norepinephrine, which influence sleep. Some types of depression are associated with agitation, which may decrease sleep, and some depressions are characterized by fatigue, which may increase sleep. Read more...