I used to work for Watts (big valve/plumbing manufacturer). Most of their stuff is brass/bronze. They run big multi-spindle screw machines 24/7 , popping out little brass fittings and other parts with almost zero labor content. Load 6 or 8 brass bars in the machine , push a button, and a few hours later you have a barrell full of finshed parts. Tooling does not wear much, little to no inspection is done therefore, there is no porosity in brass bar stock, and there is no engineering needed (parts have not changed for 100 years!). Each machine is dedicated to making one part , or maybe a few vaiations. Now with forged steel or cast iron, you have a lot more tool wear resultng in work stoppages. Someone sort of has to watch over the machining process. Iron castings are sometimes full of porosity, resulting in more scrap. There are typically a lot more workholding issues with castings and forgings, and often they will require manual loading/unloading on the machines. Definitely not an unattended 24/7 operation. All these materials are fairly cheap. Brass/bronze has one big advantage, in that it is more easily melted down and cast into other parts such as large bronze valve bodies. Watts for one, has its own bronze foundry on-site so all those brass machining chips get recyled immeditely into new bronze castings. Usually the steel and iron go to a recycler, since the ferrous casting and forging process is not as easy as for brass/bronze. Maybe these are some of the answers.
wait for it 
