Also, they simply don't want you to know. Especially if the whole setup is already a patchwork of sensors that barely work together in the first place. It might cause unnecessary questions, concerns or even liabilities.
A lot of it is useless anyway as long as the car is not broken, and if it is broken, the sensor might be broken too. It's meant for diagnostics only.
They want it to be known, otherwise there wouldn't be fail codes output to the OBDII port....
That's only there because it's required by law since 1996, and only a small subset of those codes are actually standardized/required. Many of them are specific to vehicle manufacturer and are only known to the public due to leaked documentation.
Auto corporations don't want you to easily have diagnostic info beyond the most basic things (tire pressure for example), they want you to bring it back to them. They don't profit off you fixing it yourself.