The answer to this question is pretty much 1986 (whether that’s a matter of “courage” or not), when automatic weapons — i.e., machineguns — were largely banned. There is an exception for pre-1986 automatic weapons, of which there are relatively few, since they have been heavily taxed since the 1930s. As a result, automatic weapons are very expensive, hard to get legally, and banned outright in many jurisdictions. Those grandfathered weapons are almost never used in violent crime.