But then you have many racks that could fail, any one of which taking the system out. So you add redundancies and now you have a small "server room" in each section of the building that needs to be clean enough to inspect devices without getting sut or coal dust on them.

Engineering is about tradeoffs.
Sometimes that means sticking enough RAM in a missile that runes out of fuel first and sometimes you run a lot of cables, but make up for it in reliability and easier maintenance.