I guarantee just the cost of parts for what was built in the article exceeds the budget for most guns used in crime. On top of that it's not at all concealable which makes it even less attractive for crime.

In places where you can walk down the street with a rifle and not draw attention, and the markets are flooded with kalishnakov based designs are very prevalent though, and were the market to get flooded, then they would be more common.

I don't think enough people are going to hand build these to make that the case in LA though.