Access is possible, complexity limits what you can do with it.
It's like having a JTAG port on a chip with a lot of test access. You can read the state of most of the gates, but now you're overwhelmed with data. Processing that data takes more resources than the system being monitored.
At a larger scale, though, this starts to work. Modern industrial plants and cars have sensors all over the place, more than are really needed to operate the system. They're there to diagnose it.
I guess evolution beats at the pace of signal to noise ratio
Evolution really looked at this big long list of gastrointestinal diseases we as humans can suffer from, and thought that traumatizing amounts of random nausea, constipation, diarrhea, and tummy hurt would be enough for us to figure out when we're supposed to be eating more nuts and less berries, or whatever the hell. I hate it.