I think it is because personification is the attribution of a personal nature or human characteristics to something nonhuman, or the representation of an abstract quality in human form.
Apple is to tree as grape is to vine.
Hair = simile
apples = generalization
“As Atticus tells Jem and Scout, a mockingbird does no harm and makes music for people to enjoy. Tom Robinson is like a symbolic mockingbird because of his innocence; he has not harmed anyone and is an admirable character who offers help to others. Because Tom is not guilty, it makes it "sinful" to harm him.”