Obviously most .22 Long Rifle re-sellers don't have a lot of money to "invest." Otherwise they would have been scarfing up .17 HMR and .22 Magnum ammo too, and while neither have been easy to find, when they are available the prices are either "normal" or not too much higher.
The re-sellers would also have started in on .223 and handgun ammo when it started appearing again. Both have been in stock for months in many stores, at decent prices. (And if a gummint conspiracy was behind everything, .223 and handgun ammo would still be as scarce as .22 Long Rifle.)
So yeah, it's easy to see why they homed in on .22 Long Rifle ammo. It's relatively cheap, and almost everybody owns a .22.
