Infrastructure should be the most resilient part of the system, that's why your organs are mostly surrounded by your ribcage and your arteries are on the inner side of your limbs. How are you going to recover from any given disaster if your infrastructure is too unreliable to deliver resources?

Sure you assess probabilities in your design, but not to the point of assuming the most probable outcome will always obtain. If there's only a 2% probability of some unwanted outcome need to consider not only the probability but what's at risk if your probability assessment turns out to be wrong, and make sure at least some of your infrastructure is bomb proof.

It's unreasonable to expect those things as the norm, it's not at all unreasonable to expect that they might occur and have some sort of contingency plan in place. You'd have to have been living under a rock for the last 30 years to ignore the possibility of freak weather events.