About 20 years ago there was a gang that made fake Brazilian R$1 coins (they must have been worth 50 US cents then, I don't recall precisely). And I have collected a couple of very shady R$0,50 coins that I'm pretty sure are fake. I collect commemorative coins so I always check my change carefully.

I don't think the materials are expensive, but the electricity required might be. So my guess is that this might make sense if someone steals the power. One guy was busted stealing electricity to mine bitcoin a few years ago.

OTOH, maybe they just do it for fun.