That's not how it works.
They don't have a big factory churning out MK16 after MK16 day and night.
The produce a set number of them, 500, 5 000, 50 000 and so on.
Then they ship those all out to the various retail locations.
While they're shipping them out the production line is punching something else out.
Then when the retail locations send in the new orders they run another production of MK16s and so on.
Airsoft, where nothing is hurt but feelings.