Why can the USPS loose packages without taking responsibility when they are taxpayer supported?

Our taxes already greatly subsidize the US Postal Service, giving them a HUGE financial advantage over other delivery services. Regardless, we have to pay them additional money to protect our investment in case one of their highly compensated employees steal our package (this happened to me when shipping an expensive iPhone overseas where i'm forced to write the contents on the box, alerting a dishonest postal worker that this is a good package to cherry pick). I was told in error by the postal worker who helped me that insurance is not available for packages sent to other countries. They did a cursory "package search" after they lost it and said they couldn't find it. I'm on disability and this loss is devastating to me financially. The USPS gets my tax money, charges huge fees to ship, and want a little extra from us on top to compensate us when they pilfer the packages we entrust to their care. A business like that deserves to go out of business.