German has also irregular demonyms. People in Zürich aren't called Züricher, but Zürcher. Same for Basler in Basel. Near Innsbruck in Austria, there is a small village, Igls. I discovered the last holiday there that people are called Igler there. And so on.
Are the irregular demonyms limited to places where Southern Germanic dialects/languages are spoken, or is it just coincidence that your examples are all in Switzerland/Austria?
Recall also that residents of München are not Münchener but Münchner.
This actually sounds like it might be related to the "Lutherian e" (after Martin Luther, the German reformer and namesake of the Lutheran church)[0]:
Up until the late 1700s, the trailing "-e" in words like "Füße", "mache" and so on were intentionally dropped in most of (Catholic) Southern Germany because it was associated with Luther's translation of the Bible and therefore considered heretical.
The effects of this are still present in German (e.g. the German word for "door" nowadays is "Tür" but "Türe" is still an archaic or rare variant you might encounter, likewise you might colloquially see phrases like "ich seh'" instead of "ich sehe"). If the places with demonyms that drop the "-e-" in places ending in "-en" are mostly in South Germany, that might explain why they differ.
Note, however, that the official pronunciation of "München" according to the German wikipedia actually drops the "-e-"[1] (rendering it in IPA as [ˈmʏnçn̩]), so "Münchner" is actually not as irregular as "Zürcher" (where the local pronunciation of "Zürich" actually drops the "-ch", not the "-i-"[2]).
