It's kinda hard to use that argument when they have this posted on their website....
Due to demand far outpacing supply, we are unable to accept new orders for PMAGs at this time. We are in daily contact with the manufacturer and will resume taking orders on PMAGs as supply catches up. Please note that current backorders will not be cancelled.
Actually its real easy to use the argument. Just as you posted. Backorders won't be cancelled. Brownell's is probably the largest supplier of Magpul stuff. Just backorder some and they'll eventually come. Yes it might take 2-3 months, but who cares?!?!?
I already backordered a bunch a few weeks ago, so hopefully they'll be shipped soon.