Don't we already have workers comp insurance laws? Other forms of liability insurance? Doesn't Amazon carry the same insurance if it's the one doing the delivery directly? Do we think levels of this insurance is insufficient in general and should be higher?
Bottom line - just because Amazon doesn't directly have this liability - it doesn't mean nobody has this liability - the sub contractors do. And if they do, they need to pay for the insurance, and if they pay for the insurance, then Amazon has to pay them more to pay for this insurance.
So the real question is... what concrete harm/problem are we solving for that isn't already solved for today.
Bottom line - just because Amazon doesn't directly have this liability - it doesn't mean nobody has this liability - the sub contractors do. And if they do, they need to pay for the insurance, and if they pay for the insurance, then Amazon has to pay them more to pay for this insurance.
So the real question is... what concrete harm/problem are we solving for that isn't already solved for today.