Because it has additional information in a file in `/usr/share/zoneinfo`. But you can still define a brand new timezone with the TZ variable. Perhaps you want

Because it has additional information in a file in `/usr/share/zoneinfo`. But you can still define a brand new timezone with the TZ variable. Perhaps you want to argue that you shouldn't be able to, but that's what it's for, as the document linked above clearly states.