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.
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.
It very well might have been delivered, but stolen before you got to it. Super likely in the Bay Area and especially San Francisco.
(Edit: Not caustic, but evidently highly acidic. Even better!)