Well just a look at my building would tell you why. I'm getting 7-8 hours a day as a part timer with the same amount of flow that 4 or 5 years ago would get me 5-6 at best. Sort runs 5-6 hours now, compared to running 3.5-4 hours back then, again for the same amount of flow.
Why? The majority of our building is incompetent. FFS, they tried a small easy sort change this monday and it crippled the building because people just couldn't wrap their heads around this simple swap between two belts. Every peak season they take our local packages and split a small portion of them to another belt to ease up the flow, and it results in missorts the entire peak season because at least half of the sorters can't seem to memorize 10 zipcodes. I hear stories of one guy going to a belt to help sweep irregs at the end of the night, and that one guy can do 3+ carts in the same time it takes a veritable army of new hires to do half a cart.
And of course it's because our new hires are treated like a revolving door of cheap disposable labor, so that's what we get, instead of the skilled smart people we used to. Last year we had a period where we were hiring 10-20 people a week and we were actually LOSING people over time still.
Basically I have no idea how UPS is making a profit at all right now.