The overarching aim for English in the national curriculum is "to promote high standards of language". (www,gov.uk publications).
The stories for 4 to 7 year olds and 7 to 9 year olds are designed to be read aloud by a parent of older sibling, to promote high level language. The stories for 9 to 11 year olds can be read aloud to or by the child. Story personalisation promotes engagement.