I think the reason is that this forum has been hacked several times, as the hackers have been able to access all the sensitive data from the password to the email accounts "some have been changed."
Therefore, restoring accounts using email addresses will make it easy for anyone who has access to those emails to retrieve their password.
I also believe that the process of recovering accounts is not merely the signing/verification of a message "there is an investigation going on."
Based on theymos' programming capabilities, I think he can easily add this feature but must have a compelling reason.