People collect things for investment, enjoyment, social interaction and to preserve the past. When it comes to preserving the past, the question of true ownership sometimes causes issues. For example, those who collect Native American bones may be in for a legal battle with Native Americans who want to properly bury them.
Those who collect for investment often collect things like coins, sports memorabilia and stamps. Collecting for social interaction often involves going to swap meets and meetings with others who also collect that item. Some people simply like something, such as Matchbox Cars or Care Bears, and they collect them for fun.