[m000]

I'd bet this has to do with capacity, similar with network equipment. If you operate below capacity, it's hard to tell apart a high priority packet from a low priority one. You will start noticing delays in low priority packets only when you start saturating your network capacity.

[bnchrch]

Actually it has to do with how international shipping rates are arbitrarily set by committee every 4 years.

Here’s a planet money episode on the topic.

https://www.npr.org/sections/money/2018/08/01/634737852/epis...