It’s because of the ecliptic.

Although there are 88 constellations in the sky, only the twelve constellations of the zodiac are located directly on the ecliptic, which is the path that the sun must pass through in the sky, so they are customarily called the twelve constellations.
The division dates of the twelve zodiac signs: The birth date of Aries is from March 21st to April 19th in the solar calendar.
In ancient my country, the sky was divided into three groups and 28 places. The three groups refer to Ziweiyuan, Taiweiyuan and Tianshiyuan. The 28 places are divided into Qinglong Qingsu in the East, Suzaku in the South and Suzaku in the West. The White Tiger Seven Constellations and the Northern Xuanwu Seven Constellations are the starry sky system used in ancient my country. Most of the constellations we call today evolved from the traditional constellations of ancient Greece. Note: The above content is feudal superstition, please do not believe it.