Most cable manufacturers are not wire manufacturers at all. It requires a significant capital investment to set up and operate a wire factory. The barrier for YOU to become a wire manufacturer is mostly the need to run the damn thing 24 hrs a day to make a profit and cover your overheads! So, unless you can sell MILLIONS upon MILLIONS of feet of wire, you're not going to be in any sort of wire business. MANY of the domestic wire operations have folded in the last several decades because it's tough to sell that much wire.
So, it is necessary for audio cable manufacturers to sub contract out their needs to one or more existing factories - their runs are insignificant compared to a typical industrial order - THUS, the prices are higher.
I have my pure Silver stranded wire drawn, stranded, and jacketed with PTFE ("teflon") for me by a small specialty manufacturer, I assemble it into what becomes Silver Lightning Interconnects. It is very expensive per foot because of the small quantities involved. By the time I'm done with the labor involved in the assembly and add in the costs of overhead and the materials, believe me there isn't a ton of profit. You can't look only at the cost of materials when you think about these cables.
I agree, some are junk, snake oil, and WAY overpriced. But not all.