i’m sure they thought if it’s not broke why fix it … keep it simple, and keep it functional. if i shot you in the head with a ball and powder gun or a ar 15 …same results. This is not star wars. you seem to forget the humans disarmed for a while as well. concentrating on spreading to new horizons. the best example is the 1911 colt it has not been changed in over 100 years and it is used in all branches of the services. if their is nothing wrong with it and it kills effectively their is no reason for change.