It's the same with some countries' names. Switzerland always has a female article in German: you can spend your vacation in France ("in Frankreich") but Switzerland requires an article ("in der Schweiz"). Same with Iran and Iraq, which always require a male article, and some plural countries (Netherlands, US). Note that the full list is quite a bit longer: https://deutschtraining.org/deutsche-grammatik/artikel/laend...

Typically the origin of such toponyms is in abbreviation of a designator (as happened for example with den Haag, where the full name is still survives in official documents), rather than proper noun, where the abbreviation becomes a proper noun.

In English this rarely survives except for odd cases such as The City of London (which is a small, legally distinct entity from what most people refer to as London). English is happy to drop articles when they don't reduce ambiguity, hence countries (Austria, Scotland, but retained in the descriptive name The United States of America) or Bend, Oregon (a case similar to Lenk).