Uncertainty has a lot to do with it. There are proposals out there that would tax ammo, some proposals about guns that may or may not include the "lowly" .22. If I crank my tinfoil hat down good and snug, I can tell you why I'd want 20K of .22: barter. Now we don't do TEOTWAWKI threads, but I can imagine several scenarios in which I'd want enough .22 to both: (1) take down small game; and (2) trade for other supplies.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.