Why are there no big bears and little bears in the zodiac?

The Greeks divided the stars in the sky into 88 constellations, of which only 12 constellations are in the orbit of the sun, which means that the sun will only pass through this 12 constellations a year (from the earth). This 12 constellation is called "ecliptic 12 star", which is what we now call the twelve constellations: the Great Bear and the Little Bear.

Ursa minor is not in 12 constellation, and the Big Dipper is certainly not in 12 constellation.