Scalpers and hoarders.
I see tons of it at every gun show I go to.
Heck, a month ago, on a Thursday night, I bought a brick of Federal for 23 bucks at Fleet Farm. They had at least thirty bricks on the shelf, I bought one and texted a friend to let him know they had some (it was limit one box). I asked the guy at the gun desk about it, wondering if they were actually starting to get more in now, he told me that they get in several cases every week, usually Wednesday, in this case the truck was late and they didn't get to stocking it until a few hours before. I asked him how long it usually lasted, and he said there was a group of guys that showed up every week. Different ones would stop in the store throughout the day, and whenever something was on the shelf they'd apparently let the other guys know because all of them would show up over the next couple hours. He said that more than once, he'd see a guy buy a brick, then twenty minutes later he'd see the same guy grabbing another brick. He said the people in the sporting goods department tried to stop that sort of thing, but that effectively the 'limit one' meant the cashier wouldn't let you buy two bricks, and that if someone was dumb enough to go back to the same cashier the same day, the cashier might say something.
Anyway, that Saturday, I was at a gun show, and a guy (actually someone that I don't know personally, but know of, as he's always got tables at every gun show in the area) had the same ammo on his table for 90 bucks a brick. And guess what, there were bits of price tag left on the some of the boxes. He'd peeled off enough that you couldn't tell what any of them had been marked at, but the bits looked identical to Fleet Farm price tags...