My DBF works for the USPS. True, morale is low, and some of the other issues mentioned are also true, but there are other things that come into play. Bubble wrap does help cushion things, but if the bubbles pop, theres NOTHING BUT AIR to cushion the item. If the tape on the outside of the box was left even a little bit loose it can catch in the machinery and then the entire box and contents can be damaged. This is true for the other carriers too. The USPS is really working hard to improve customer service - it may be worth a visit to your local PO to talk with the postmaster there. If you go at a less busy time of day they may have more time to help you. These can things happen with all the carriers - my BF's brother works for UPS and says they are having similar issues.
Sadly I purchased a cute li'l child's singer from an ebay seller who packed it by nestling it in a box filled with packing peanuts. Well... they shifted, the machine slid and the thread pin poked through the box and was badly bent. This is from a seller who had a great rating. In this case it's clear the packaging was the problem.
It's hard to know for sure how the damage happened to your motor, but the postal workers I know (and I know lots of them!) DO really care. They truly don't want to deliver anything that's been damaged.