It feels like given that Amazon give you no agency in when the package arrives, and also no guarantee of forewarning, then they've given you no option to prevent the package remaining on your doorstep, the liability should morally lie with them.

(Legally, could be more cloudy depending on jurisdiction, but I'm sure their tendency to say packages will require a signature on delivery but then to leave them on the doorstep with the driver's signature alone probably does them no favours)

Amazon leaves the package on your doorstep because it's slightly more convenient for you and WAY more cost effective for them than the old-style "we missed you; come pick it up at our location in a day or so" note. No physical location in expensive areas, no repeat deliveries, no hauling & managing packages coming back on trucks. When you buy something from Amazon they have not delivered it by throwing it on your doorstep. Ironically we never would have taken delivery of expensive purchases like this back in the day when the world was so much "safer"...

If you have video evidence showing that Amazon just left your package out in the open then someone came up and nabbed it I'm sure Amazon would just send you a replacement if only to keep you happy as a customer.