I have no idea - because everything you’re arguing against makes it make a lot more sense to add it to the vendor. Literally everything you are saying it just “because it shouldn’t be added” instead of actual reasoning. What’s the point in not adding the Embers/Cinders to the vendor besides you just saying so?
If your guild is only NOW completing one, they haven’t been raiding this entire time. Even on 10 man.
Raiding every week on 10 man - even on NORMAL - would make you almost 4 staffs in a 12 weeks period. We are 15 weeks in.