Because we sell all our precious metals to china and then buy them back
Seriously though when you check muffler shops and labor rates for custom bending something up and realize you are still looking at $400-$500 in most cases, and then see that you are getting a "crush" bent system with cheap universal hangers, then you see the aftermarket bolt on kits are a pretty good deal.
Mandrel bends, larger piping than the factory ever offered, and most applications on a good system will also include factory style hangers as well. I for one won't hesitate to pay upwards of $6-$700 for a good kit when I know it fits well and performs well. In most cases it's the last system I'll ever have to buy in my lifetime.
The Pypes systems have been some of my favorite setups to use and install considering the money you pay, for stainless steel mandrel bent, stainless mufflers too, "X" cross over, and factory style hangers all for $499 on most muscle cars I've done,,,,hard to beat for the price. Engineered well and fit has always been excellent on F-bodies, X-bodies, and A-bodies that I have installed.
I've paid more for other systems that didn't fit worth a damn and took alot of fab work, not to mention were made of aluminized piping and aluminized mufflers. So I feel I get my money's worth on the Pypes systems. Cheapest stainless setups I've seen out there and they sound great too.