Reporting of accounts is at the creditor's discretion, depending upon whether they want to make the information about your past credit history available to others in their evaluation of your credit risk. That is the altruisitic, "good of the system" reason for reporting.
The more practical reason for creditor reporting is to place incentive upon their own customers to pay timely, or to pay delinquent debt. They know you read your CR and are concerned about your credit score, so it becomes more than just an altruistic "good for the system" motive. It helps "keep you in line."
So, given that there are different reasons for reporting, there are also different reasons for not deleting. Only the credtior who reported the information can delete their reporting. The CRAs dont delete on their own initiative, except for those accounts that have reached over 10 years from date of closing (a nasty and questionable CRA policy).
When an account is closed, reason 2 is kinda gone, as they no longer have an active account with you. So they wont care about the practical aspects of their reporting, and deletion would not impact them. However, technically, the altruistic reason 1 still applies, and deletion would deprive other creditor of a complete view of your past credit history.
So they could legitimately set a policy not to grant deletion of prior, accurately reported information. Who knows how any individual credit will view deletion of their reporting when requested to do so by a former customer? Not much in it for them..... so maybe offering some good-will reason why it might benefit them, if you can concoct such a reason, would help.