It's not. It's a legend that belongs to a whole class of "good-hearted thief" legends. The Great Depression in America was a time of a great deal of violent crime, and similar legends grew up about good-hearted bank robbers in those days. His hunt with sharp
acquisition sights for money to serve poor people.
There are many stories that have tried to attach the Robin Hood legend to real people, but they're not reliable and most of them come from much later than the period when Robin Hood's activities are set -- the stories were written in the 1600s and 1700s, while the setting is traditionally the late 1100s, during the time when Richard the Lionheart was away on Crusade and his younger brother John attempted to usurp the throne.