There's always some risk that infrastructure will catastrophically fail, and in general I think a month-long self-sufficiency stock is a perfectly reasonable thing to have. (I have one myself, although primarily because I live in an earthquake zone.)
But when people are reacting to the coronavirus, the implicit question isn't what preparations are good to have for general worst case scenarios; it's which preparations you're likely to need, which ones you can no longer afford to be without. As many a doomsday prepper will attest, there's always one more contingency you could plan for, but telling people to start with extreme measures makes it less likely they'll plan at all.
But when people are reacting to the coronavirus, the implicit question isn't what preparations are good to have for general worst case scenarios; it's which preparations you're likely to need, which ones you can no longer afford to be without. As many a doomsday prepper will attest, there's always one more contingency you could plan for, but telling people to start with extreme measures makes it less likely they'll plan at all.