ISO 6801 gives the date as YYYYMMDD but also allows the inclusion of dashes for visual clarity such as YYYY-MM-DD. This format is also (as IICIH illustrated with his little song) called "Big-endian". I like this one because, as Sitnspin pointed out, if it's in numerical order, it's in chronological order as well, so it is very useful for indexing. It's written left to right with the most significant digits on the left just like any other numbers we write. It is, its way, elegant.
Little-endian, DD-MM-YYYY, is more intuitive for conversational use. It truncates very well in casual conversation. If I ask my librarian for a copy of the newspaper from the 23rd, they'll very likely assume I mean the 23rd of December. If I say that I need the paper from the 23rd of November, they'll very reasonably assume (as you did in the last sentence I am sure) that I mean November 2020. So it makes sense to use little-endian order since the most relevant information is closest to the front (in most casual applications).
Middle-endian, MM-DD-YYYY, is only used in the US, as far as I know. And not without good reason. It isn't simple or elegant. It makes no sense. Why do we do this? Why are we so stubbornly foolish? It is the same reason we do anything. Someone did it that way once and it stuck and we're too embarrassed to admit that we've been wrong this whole time.