Did I see an idea for a bolted-down secure box that only the delivery person has the code for? (Could be on their phone, for example). Seems like the obvious solution..?
Yes, they have those (at least in the U.S.). My neighbor has one. In a dense city neighborhood with narrow sidewalks, the box can take up a bit too much of the pathway for pedestrians, but other than that it seems to be a good solution. The real challenge is finding a way to ensure that all the delivery people have the code. US Postal delivery people rotate on urban routes, and Amazon's own delivery service - a major source of theft because they're the main ones who leave packages exposed on doorsteps - has a constantly rotating cast of per-job delivery people who are just regular folks picking up delivery shifts.
I suppose if some consistent system can get created where the code can be printed on the mailing label of the package, that would solve the problem - no matter who the delivery person was, they could see the code on the label, and once the package was put inside the locked box, having the code on the label wouldn't be a security concern.
Here in the UK we have a very simple solution: don't leave parcels sitting outside. The delivery driver knocks on your door. If you don't answer, he leaves a card in your letterbox, so you can arrange a new delivery or pick it up from their depot. If can't be home during the day, the simplest option is usually to have stuff shipped to your workplace.
In the U.S., the US Postal Service tends to do just that, as does UPS. Fedex Ground/Home Delivery, however, routinely leaves the package exposed rather than a pickup/redelivery slip - and Amazon Logistics (really just a series of individual delivery people who do per-job contracted delivery for Amazon) doesn't even offer pickup slip/redelivery as an option. Ditto for DHL Global, which is a division of DHL that specializes in cut-rate residential ground delivery.
In addition, the major private delivery companies have consolidated (read: reduced) their hubs in recent years. They are compensating for the lack of hubs and the package-theft problem by designating "Access Points" like UPS Stores, mailbox stores, and just regular businesses where customers can have their packages delivered, for pickup later.