Demand for expedited shipping has fallen every year since 2021. At UPS, average daily volume for domestic next-day air services fell 7.1% in its most recent quarter, compared with the prior year.

With one-day shipping, every minute counts. UPS can’t afford to waltz to the deepest depths of its warehouse, one item at a time, and expect to get it across the country in 24 hours.

Despite cutting 20,000 positions and automating work at 400 facilities, UPS says the changes to its operations will not affect the experience of customers. But for the U.S. Postal Service, some ...