The addition of an extra day in a leap year is a peculiar quirk in our modern calendar system. While the concept of leap years has been around for centuries, the choice of February as the recipient of this extra day has historical and cultural roots that trace back to the evolution of the Roman calendar.

The Roman calendar, which heavily influenced the development of the Gregorian calendar we use today, originally had ten months totalling 304 days. These months alternated between 30 and 31 days, with a winter period not assigned to any month. As a result, the calendar was out of sync with the solar year.

When the Romans decided to reform their calendar to better align with the Earth's revolutions around the Sun, January and February were added to the beginning of the calendar year. February, with its 28 days, became the last month of the year. The Romans, considering even numbers as unlucky, opted for an even number of days for February.

(This is because of a simple mathematical fact: the sum of any even amount (12 months) of odd numbers will always equal an even number—and the Romans wanted the total to be odd. So, they chose February, a month that would be host to Roman rituals honouring the dead, as the unlucky month to consist of 28 days.)

The addition of an extra day during leap years is a continuation of this historical convention. While any month theoretically could have been chosen for this adjustment, February was the month selected during the gradual development of the calendar system.

It's crucial to recognize that the choice of February might seem arbitrary, and indeed, it is a historical artifact. The Romans and subsequent calendar reformers likely did not foresee the significance that this decision would take on in our modern era. However, once established, traditions tend to persist, and changing the allocation of the extra day would require a substantial overhaul of our timekeeping system.