I moved from Vermont to Virginia in 1975. About 1984 I rec'd a Christmas card from my mother, sent in 1975. Post Office had lost it for a few days.

I think that they deal with a very large number of packages and if the shipper does not think that the package is worth tracking, it's loss is not that important.

I have made a policy of NOT buying stuff online if it costs more than a few $$ and will only be shipped USPS, it is too much of a crap shoot.