Sorting with either the month or the day ahead of the year results in more immediately relevant identifiable information being displayed first. The year doesn't change very often, so it's not something you necessarily need to scan past for every entry. The hour changes so frequently as to be irrelevant in many cases. Both the month and the day represent a more useful range of time that you might want to see immediately.

Personally, I find the month first to be more practical because it tells you how relatively recent something is on a scale that actually lasts a while. Going day first means if you've got files sorted this way you're going to have days of the month listed more prominently than months themselves, so the first of January through the first of December will all be closer together then the first and second of January in your list. Impractical.

Year first makes sense if you're keeping a list around for multiple years, but the application there is less useful in the short term. It's probably simpler to just have individual folders for years and then also tack it on after days to make sure it's not missing.

Also, like, this format is how physical calendars work assuming you don't have a whole stack of them sitting in front of you.