I don't know 22 has always been popular, as a kid my Dad and I was always out shooting them. The only time we shot anything else was hunting or shooting clay pigeons. Dad had I nice collection but it was dominated by 22s, I guess even back them it was cheaper guns and ammo alike. And they are just so fun to shoot. The first rifle I ever shot was a lever action 22 I can't recall the manufacture but it was called a palomino. The first pistol was a 22 hi standard hd military.
yes, all the factors point toward the .22lr being the most popular round of all time. affordable prices for guns and ammunitions. quieter, less recoil, easy to learn on and fun to use after learning. i will probly own a few more .22s in the future and i already own about 5.