Why is astrology based on date of birth and not conception?

It is believed that the moment of conception does not have a serious effect on the zodiac sign. Even in ancient times, the embryo was considered a part of the mother's body until the child was born
If astrology is a science, why does the daily horoscope show truth and then nonsense?

Astrology is based on the language of archetypes, which people interpret themselves, so interpretations can vary. The position of the Sun at birth, for example, at the beginning and end of the sign is very different, so the recommendations look quite general. Besides, astrology is not only horoscopes.
And why all the focus on signs, if horoscopes are so complicated?

The zodiac sign is the base on which the foundations of the personality rest. For more accurate forecasts, it is important to know your moon sign (it is closely related to emotions), as well as the rising or ascendant (it shows how a person sees himself). And they all depend on the place and time of their birth.