Because you are intentionally oversimplifying or purposefully lying. AR 15 is modular platform that comes in dozens of different calibers from hundreds of different manufacturers. There may still be some 22's from armalite available but the bulk of the ARs will be in .223/5.56 but you can also get them in 300 blackout, 6.5, 9mm, .458 socom,...... My favorite is the 6.8 SPC. To say the AR 15 is an armalite 22 is like saying the one dollar bill is money. Kind of ignores the other denominations and worldwide currencies.