Hi,
The name collision might not be the (only) reason,
both my menu item and archive folders are named "Archiver".
But it is still possible that Mail.app displays a short name for my archive folder, i.e. "Archiver", and internally refers to it as something like "gmail/Archiver".
There is a lot of guessing involved, I'd love to see someone that is knowledgeable jumping in the conversation.
EDIT:
Why keyboard shortcuts matter?
keyboard shortcuts improve your productivity alot and save you time!
How much time does it take to reach your mouse, click on the subject then click on the archive button. Probability not long: 1.5s,2s... But repeat it about 50 times in a day.
Multiply by the number of work days in a week and then in a year. Finally multiply it by the number of years you still need to do until retirement.
Now, consider you save 0.7s per shortcut use and say thanks to the one that will find how to enable that shortcut.
Cheers,
Quentin