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.
One of symptoms. There are multiple symptoms related to depression. One of symptoms is excessive sleep.