Here's why:

* Solar year: The time it takes for the Earth to complete one orbit around the sun is approximately 365.2422 days.

* Lunar cycle: The lunar cycle, or the time it takes for the moon to go through its phases, is approximately 29.5 days.

* Calendar alignment: The 365-day calendar aims to synchronize with the seasons, which are determined by the Earth's position relative to the sun.

While some ancient calendars were purely lunar, the 365-day calendar is a solar calendar designed to align with the Earth's orbit around the sun.