Because penetration is spotty at best, especially through clothing or other barriers.
Because rimfire rounds are inherently less reliable than center-fire.
Because the goal in a defensive shoot is to stop the threat as quickly as possible and there are many many better options for that purpose.
Because other calibers exist.
Because I'm not willing to bet my or my family's life on a physiological stop.
Because Appleseed ammo shouldn't be wasted on mopes.
Because etc.
Exactly!!! ^^^
OP needs to do some online research about the ballistics difference between .22 LR and 9mm, .45, .40, etc. A large man will not be phased by a .22 unless you just so happen to hit him in the eye... And if he's wearing a thick leather jacket and other clothes, I doubt the .22 would penetrate and do any significant damage... 1,200fps is not hard to stop when the lead is the size of a pencil eraser...