Gun barrels come in all kinds of different hardnesses, as does lead and jacketing material.
Take a standard “copper jacketed” .22 bullet and cut it in two with a pocket knife. You won’t find it to be very difficult to do. Next, try doing the same with a metal jacketed .223. You’ll find its hard to do.
High pressure bullets need to be hard, so that they won’t blow out, low pressure bullets need to be soft, so they will seal.
OK, I get that. But why make a 22 barrel softer? I’m not being argumentative here, I just don’t see any reason to do so, except maybe cost.