Federal law prohibits any government entity from classifying air guns, muzzle loaders, bows, crossbows, or wrist rockets as firearms.
I don't understand the trend either. Almost half of my airguns are .22. I have 7 .177s and 6 .22s, soon to be 7 .22s. If the trend continues, I will get a QB78 deluxe .22 (tuned by mike), a TF89, a Benjamin-Sheridan 392, Benji pump and CO2 .22 pistols, a Crosman 2240 or 2250, and if I'm really lucky, an Air Force Condor .22.
Of course, there are more .177s that I want, also I just prefer the .22 because it's more powerful for hunting, and the pellets are easier to handle with my thick fingers, especially when they're cold and nearly numb.