I notice that the incidence of poisoning from the activity of Clostridium botulinum is quite rare. For example, in 2015 there were only 7 incidents of foodborne botulism poisoning identified even though only nanograms of the toxin are enough to cause illness. By comparison Salmonella causes over a million illnesses every year.
The sensitivity of Clostridium botulinum to oxygen is one possible explanation, but it would seem to me that there should be enough anaerobic environments that Clostridium botulinum should be able to flourish anyway. Is this the main environmental limitation that affects Clostridium botulinum, or does it have other fragile life requirements that cause it to rarely occur in nature? If so, what are the conditions in which it persists?