Amazon Locker on the porch is one solution, but as others have pointed out it won't work for everyone and it's also not scalable for all deliveries the way some other general solutions for delivery people might be.

What they have now is, I think, a choice some people might still make given the trade-off: is Amazon more likely to abuse the key you give them? or are your packages more likely to get stolen off the porch? I've lived in neighborhoods where that cost-benefit would make total sense.