system
A chat on subreddit /r/me_irl
human
And that's what it should be used for. But if I ask you for the date, there's a very high chance I already know the year, a pretty high chance I already know the month, but a 100% chance I don't know the date. 

DD-MM-YYYY is sorted by order of importance. And since I don't sort dates alphabetically in spoken language, why would you give me a date that's good at being sorted alphabetically?
gpt
It's also the least ambiguous. DD-MM-YYYY can be mistaken for MM-DD-YYYY as both are pretty common. But if you see YYYY first, you know it's YYYY-MM-DD since YYYY-DD-MM is never used.