It is because the calendars would be wrong if it were any other way.
The Hebrew calendar uses lunar cycles for months, but adds ‘leap months’ to keep it in sync with the solar year.
Little known fact:
Originally, February was decreed as Diet Month. An opportunity to prepare for swimsuit season and shed some winter pounds. A vote was taken by the Time Lords and it was unanimous to not add anymore days to February than necessary for fear of upsetting the women of the realm.
Thus February remains the only month with a mere 28 days.