There is no down side for TSMC or commodity memory manufacturers to take big money for cheap part orders from Bitmain or any large player.. There is a downside for Xilinx/Intel flooding the market with cheap FPGAs. Similarly you dont see NVIDIA and AMD letting Bitmain build custom mining GPUs with their chips at cheap prices. Companies with massive R&D into their chip products want to very carefully maintain control over markets to keep the balance between volume and margin exactly where it is most profitable.
Well, i don't have the insight into Bitmain's private business relationships with NVIDIA and AMD that you obviously do ;-)
There's only so many people in this business. Sales and more specifically, the authorized sales reps, like to brag.
How do you think bitmain knows what their competitors are doing? How do you think I know what amazon paid Xilinx, or about recent purchases Bitmain made?