The beauty of it for Amazon is they only need to compete in their best markets. Pure shipping companies have to go everywhere, but Amazon has the luxury of doing its own delivery only where it is easy and outsourcing it to legacy shippers where it's not. For example, I could easily see Amazon delivering directly to large condo/apartment buildings in urban areas.
Only USPS ships everywhere. If you go to UPS/FedEx/DHL, they will tell you they ship everywhere and take your package, but if they deem your package not profitable enough they will hand it over to USPS.
The shipping market is incredibly complex with USPS and FedEx actually being each other's largest customers.
That is true, but it is also true that UPS and FedEx still operate a lot of non-profitable areas. They rely on easier metro areas to help subsidize the losses.
This already started to happen a while ago (couple months?) in Munich. Amazon packages are delivered by a specific Amazon delivery person instead of DHL as before. Now I don’t need to sign anything any more when at home and when I’m not at home, it will be left in front of my apartment door; whereas DHL either handed it over to a neighbour or a ‘closeby’ post office.
Not sure what I would do if a shipping went missing while in front of my apartment door, but from past interactions with Amazon, I’d assume they send a new one without asking questions.