He might want to reuse his email with a different username that is why he wants it to be deleted.
What's the point of creating another account with a different user name and the same email when he can just use this one until there is a need for him to request a change of username, or probably he can just create a new one with a different email, which he can create and start all over again if there is no post or reputation created with this one for the main time?