The systems used by USPS compared to other package shippers are quite different. Historically, USPS has not affixed scannable barcodes to every package, at least not the type that would be required for tracking software/systems. Whereas with UPS, for example, their entire network is built around that label that is generated and affixed to
every package per their system requirements. And all of that is done by scanners and machines. (Try walking into a UPS store with your Christmas present wrapped in a grocery bag with a handwritten address scribbled on a scrap of paper and attached with Scotch tape, and then ask them to insure it for you!! That's something that happens all day long every day at the Post Office).
But the USPS is in the process of transitioning to something like that type of process (i.e., trackability/visibility for all packages). So right now, they're
supposed to be scanning every recordable type of label that comes in the door, whether at acceptance (origination) or for final delivery. It's not something they've done before, so you can expect that the transition will have its hiccups. (Keep in mind, if you don't print your own labels--with some kind of confirmation, or don't purchase insurance or confirmation at the counter, by choosing to save a couple bucks
you are assuming all the risk. Tip: spend the few dollars for insurance.) It's worth noting too that packages aren't all that they handle. In fact, the USPS delivers more articles every single day than UPS and Fedex do in the entire year. In my experience, you can usually count on great point-to-point scanning from UPS, as much as you can count on them delivering the crushed and mangled--and scanned(!!)--box right to your doorstep! That's my three cents' worth!