Part of TSMC's offer is that they won't do design, they won't compete with you on design etc.
They specialize in the best possible fab and service for your design and that's it.
That's kind of a hoax. GUC (Global Uni Chip) is huge, and a nearly-wholly-owned subsidiary of TSMC.
https://en.wikipedia.org/wiki/Global_Unichip_Corporation
TSMC has a large design operation. It simply is part of a subsidiary rather than the parent company, that's all.
There are a lot of shady links between TSMC and GUC. I was once pressured to "collaborate" with GUC as an explicit condition of getting access to the then-bleeding-edge 16nm PDK. I turned it down. A competitor of mine (with whose chief engineer I am friends) had the same screws put to them.
Imagine 100x of that, and that is Samsung.
There's a lot of interest in that from a national security perspective anyway.