My neighbor is a hoarder. Many animals hoard by nature, and they say human hoarding may be related to that but there is substantial evidence lacking there.
My sister and her husband are both hoarders of things.  they love to buy in bulk and just continue to keep everything they buy therefore their house is full of stuff
Compulsive hoarding
Compulsive hoarding, also known as hoarding disorder, is a behavioral pattern characterized by excessive acquisition of and an inability or unwillingness to discard large quantities of objects that cover the living areas of the home and cause significant distress or impairment. Compulsive hoarding behavior has been associated with health risks, impaired functioning, workplace impairment, economic burden, and adverse effects on friends and family members. When clinically significant enough to impair functioning, hoarding can prevent typical uses of space, enough so that it can limit activities such as
) One theory suggests that human hoarding may be related to animal hoarding behavior, but substantial evidence is lacking.
Human hoarding.
Civil unrest or threat of natural disaster may lead people to hoard foodstuffs, water, gasoline and other essentials that they believe, rightly or wrongly, will soon be in short supply. Survivalists, also known as preppers, often stockpile large supplies of these items in anticipation of a large-scale disaster event.
Human hoarding Anxiety disorder and hoarding.
Individuals who meet diagnostic criteria for hoarding