One of the largest markets for replicas is the entertainment industry. Which uses squibs, blanks or other methods to make it look like they were fired. Which without modification can cause serious injury or death.

Having a pistol that can fire a low charge blank doesn’t need a fully hardened barrel, which on some is easily replaced. As an example.

There is also the ability to make someone think you are holding a firearm that could cause them harm (easy if the person isn’t infantry qualified), especially during a robbery.

These people didn’t have them to put them in a shadow box, they had them to appear more dangerous, which can push them into the terrorist designation.