I guess it didn't jump out at me, because I work in the shipping industry. It's like if someone said "hah, look at that jeep, it's got a fifth wheel attached to it's rear gate! Is it expecting to drive at a 90 degree angle?!"
It's not a quirk. That is on purpose. In the shipping industry, the estimated delivery date is based on the date it was shipped, not on the current date. Things would get messy if the ETA was constantly revised.
A "revised estimated delivery date" may make things less confusing to a consignee. But if your shipment is already outside of your expected delivery window, it's not always feasible to give a new ETA.