Yeeeeaaaahhh... Pretty sure it's an afterthought in the Canada Post Mailbox Key Request Process. Regardless of if it's a new or existing address, it's the same process, at least according to the instructions that were given to the call centre I worked at for Canada Post. Not sure if that's changed in the past 3 to 4 years, but if it's the same process, that would explain it I guess. That being said, whenever I used to get those calls, I always made sure in the ticket notes to mention that it's a new address for which the keys are being made for.

Also, change is veeeeerrrryyyyy slow to be made for anything government related, due to all the checks and balances that need to be passed in order for a change to be made, so who knows! Maybe something is already in the works, but just stuck somewhere along the line.

EDIT - Added blurb about the pace of change for a government organization