How can this be the case if for something far more direct-to-the-gut like cooking, the process of heating your food to about 75°C for at least a few seconds is enough to kill every known pathogen (except maybe prions, not sure about them).

Given that, why would you need 121°C, let alone 232°C to sterilize things like compost?

I know that high temperatures don't destroy all known microbe-created toxins, but then, that's not the definition of sterilization, which is about simply destroying the pathogens themselves.