I’m not so sure that it is a case of “too much bother” so much as a case of destroying evidence. The efforts to recover any information will be full of sound and fury, perhaps even frenzied activity, but will (intentionally) come to naught. Even IF the e-mails are found by someone within the administration, I’d bet those files will be (illegally) purged as well.
That’s why the quotation marks. It’s an excuse I thought I actually saw. The IT system probably is not designed, as it is, to be able to hunt for an email in backups without intensive manual efforts. Files are stored by file name but there is no attempt to index contents for the sake of the backup media.