Except they don’t seem to be. Most users don’t seem to be seeing this - the URLs I gave you are supposed to be for the file used by default, out of the box config. And it is - I just set up an iPhone SE today and it knew Easter was coming up.
Strange, my iPhones are definitely “default” for holidays, and I have no recollection of changing the “.ics” on my Mac Pro, yet no Easter. Will have to check and see what the default is supposed to be...”...//p14-calendars.icloud.com/holiday/US_en.ics” or your link or something else???