Amazon might be smart enough to deliver packages in the evenings when people are home, something FedEx and UPS just can't quite get their heads around.
To deliver in the evenings on a large scale they'd have to compress the work they do in the 8-9 hours of the normal working day (more in some cases where they do actually deliver in the evenings giving them almost 12 hours of delivery time) into the ~3 hours between 6-9 (starting at 6 because who actually gets home at 5 with commute times). All that goes to say if you want evening deliveries you're going to have to a lot pay more for deliveries just because it will require a lot more drivers (who will want better pay for working evening when they'd otherwise be home).