Most people don't go out and blow away 300 rounds of shotshells in an afternoon (unless they are heavy-duty clay bird shooters). Lots of people shoot up a brick of .22 LR in an afternoon. Thus, shotshells are far more available on shelves than .22 LR. Plus, if survival fears exist (as I feel is the current belief), one can carry, hide, etc. far more .22 RF ammo than 12 Gauge shotshells, .38 Special, etc. So people instinctively want more of it. And the .22 LR is not nearly as puny and inadequate a defense/survival caliber as many seem to believe it is.

In a true EOTWAWKI situation, I would rather have a good .22 handgun, a .22 rifle, and 10K rounds of .22 ammunition squirreled away than any other survival armament arsenal. And I think that is the reason for the current .22 ammo shortage.