It's an easy answer made complicated by bacteriology in general and dairy science and contamination specifically. To put it simply, the combination of raw material, handling, bacterial ecosystem, and affinage make it difficult for botulism spores to gain a foothold and to grow.
Botulism requires a nutrient-rich medium, one in which it can move, and one that has good conditions. Those good conditions are a low salt content, a high pH, and proper temp. Cheese matches few of these, and moreover, cheese bacteria tend to outcompete botulism.
For example, during the initial stage, when milk is fresh, those lactic bacteria multiply so quickly that botulism never gets a chance. And if it did get a chance, the acidity becomes low rather quickly. And then after the acidity, there's the salt. Botulism is inhibited at 4-6%, and I'm talking about pretty drastic inhibition.
Then after that you're stuck with a pretty solid block of protein and fat. If botulism is inside, it has little food. It's not like soup or processed cheese. And it can't move to find food.
And then suppose you have spores on the surface due to post-make contamination. If you do that, ok, then there's a chance. Except not. What would they eat? Nothing, the rind is dry. And it has all sorts of bacteria and molds on it, and yeast, even when vacuum packed. And then you have the affinage. After a couple of months, it's not really an issue anyway. And the botulism can't ever make enough toxin to be a real issue. In washed rind cheeses, it's possible, except in classic washed rind, you have many generations of bacteria that kill spores. b linens, S xylosum, etc.
So there you have it. If you approach it from a HACCP point of view in terms of the contamination vectors, it's tough to contaminate. Even if you do contaminate, there's so much stacked against botulism that it can't grow. It's not simple, you can't just say, just because the environment is anaerobic, botulism will grow, or because the pH is a certain level, it won't grow. You have to look at the bacterial ecosystem, the media, and everything else, to make a determination of risk vector and threat probability.