I'm pretty comfortable with the FAA using strict methods to avoid that scenario.
Recently Amazon has starting using the USPS to deliver more packages (or at least the last-mile delivery), and that service has been disappointing, I can usually count on a USPS package being delivered at least a day late, and more than once, it hasn't shown up at all, despite being marked as "delivered at front door".
In any case, while I would think that any unhappiness between UPS and Amazon would be resolved through their contracts, I doubt that UPS wants to rock the boat with Amazon, because even a small piece of the Amazon delivery pie is a lot of deliveries. So in this case, where workers health and safety is in question, it's good that the government stepped in to prevent UPS's desire to keep a customer happy from getting in the way of their worker's welfare.
It very well might have been delivered, but stolen before you got to it. Super likely in the Bay Area and especially San Francisco.
I originally blammed Canada post but perhaps this is an AWS shipping issue after all.
Amazon has always been quick to ship out replacements when I reported the missing packages (even when the USPS said they were "delivered"), and even for the one that was re-delivered by my neighbor, when I reported to amazon that I received it, they said I could keep the $10 item, no need to return it.
(Edit: Not caustic, but evidently highly acidic. Even better!)