I am convinced it's the hoarders (I call them hogs) that are causing this issue. I live in PA and every day, the same group of three or four clowns line up at the local Wal-Mart before the clerk brings out ammo at 7 am, and scarf up their three boxes of whatever, leaving little for everyone else. How do I know this? Well, I go there when there actually is something I am interested in, and guess what, by the time I get there, the same folks are in line. I already complained to the WM manager that they should impose a 3-box, 1-box-per-caliber limit, so that more people will at least get some ammo. In fact, I plan to write W-M and suggest same.
Honestly, this "shortage" has given me a jaundiced view of some of my shooting brethren. I am not impressed.