Turns out that .223 ammo, cleaning gear - heck, AR-15s themselves - are in short supply. There's been a "panic buy up" of all weapons and ammo that might come under any kind of "assault weapon ban." Just the hint of a 2nd Amendment-hostile administration is enough to get the guns flying off the racks.
This is a good example of the law of unintended consequences. The mere hint of "assault weapon control" (based on what a gun looks like, rather than any statistical association of a particular weapon with real crime) is actually putting more of these weapons into private hands.