The correct answer to this open question is the following.
The possible reasons why there are so few literary milestones recorded for the early years in Britain could be that most of the stories of that early British years were passed via oral tradition.
People memorized the stories and were passed orally to other people, families, and further generations.
The name historians have is "oral art form." Experts had to write the manuscripts by hand. It was not an easy task and was a slow process. Not all knew how to write, so it was most common to tell the stories than to write them. That is why there are so few literary milestones about the early Anglo-Saxon period.
