I think formats with month and day before year are popular (and possibly emerged originally) for cases in which the year's only really included in case you're not sure whether you're reading something old and the date's already passed, that is, the date is referring to something 12 months or less away, which is probably a very high percentage of dates people encounter day-to-day. This puts the most useful information up front. The alternative being dates that omit the year entirely, which are also very common.