Answer: Because bakhars of medieval times contain accounts of historic events, battles and lives of great men.
Bakhars contain eulogies of heroes and stories of events. For example, ‘Sabhasad Bakhar’ by Krishnaji Anant Sabhasad gives information about the rule of Chhatrapati Shivaji Maharaj, ‘Bhausahebanchi Bakhar’ describes the Battle of Panipat and ‘Holkaranchi Kaiphiyat’ tells about the Holkars. Bakhars are of many types: biographies of kings, dynastic histories, descriptions of events, etc. Hence they are an important source of history.