That happens mainly from two things. Most carriers take the letters to the street, unseen(it's called DPS, delivery point sequenced, supposed to be 97% perfect), plus the pressure of excess parcels that are hard to deliver timely. We used to concentrate on regular mail, getting people their letters and magazines on time and without mistakes. Now the powers that be don't really care about regular mail, they spend most of their time finding enough people to carry the parcels and get back before the last mail pickup truck. They concentrate on parcel scans, so none are left behind on purpose or accident. Then there are semi-regular meetings about how not perfect the parcel deliveries are, no mention of regular mail, or customer service(mail on time and correctly etc).
My route two weeks ago they didn't schedule anyone on it, and called me to ask if I'd come in on my day off. I couldn't, so they put off my route in the morning, just having one person case the small amount of raw mail, and two to deliver the parcels. The next day I came in to see my case with about 15 minutes of mail in it, which on the street added maybe five minute to my day. There were about 6-8 parcels left in my large wire container(characters written on them, all the subs do that for every parcel(so I knew they were from the day before)). When I was done sorting my parcels and ready to tray them up to load, I came back after preloading my large parcels, to see two trays of DPS on my desk. That's when I discovered they literally had nobody carry the mail the day before. I spent another 30 minutes casing that DPA from the day before, and it added about 10-15 minutes more to my day. So that day I spent almost an extra hour doing the route, and only got extra pay for the two trays of DPS, which pay us .0333 minutes per letter. That would be about 25 minutes for two trays generally. That's how well or PO is working in my office, it's likely that bad in all cities where most Amazon goes through the USPS.
