Why is the Postal Service so sucky?

I grant that the postal service does a good job at delivering letters. But give them a package, and you'll mostly likely not see it again.

Why is it if I try to track a package from UPS or FEDEX, I can basicically tell where this pachage is within about 10 feet in realtime.

But if you try to track a package via USPS, it will not even have record of the package until about a week after it was already delivered.