It's also unambiguous. Nobody uses yyyy-dd-mm, whereas xx/xx/yy can be misinterpreted.

I distinctly remember SQL Server 2000 pulling that one on me. I had switched a DB app over to using ISO dates exclusively in its queries to avoid the month-day-ordering confusion and then the bloody thing earnestly started to parse yyyy-mm-dd dates as yyyy-dd-mm at every chance it got. So much for unambiguous date formats!

Apparently, Kazakhstan uses yyyy-dd-mm, but only in Kazakh (not in Russian.)

I guess if we are only talking about English speakers, that’s not an issue, since if Kazakhs don’t write dates that way in Russian, I presume they wouldn’t do it that way in English either