12: They have more moons because they are bigger. They have a greater gravity field so they pull more on other objects. Gravity is like a blanket held taunt. If you put a big bowling ball in the center and place an orange on the outside the orange is going to want to go to the center, where the bowling ball is. Now if you add angular momentum to the equation you get gravity. Of course it isn't that simple but its the jist of it. Therefore, since Saturn and Jupiter have a higher gravitational pull on other celestial objects they pull on more matter around them, like asteroids and such. These asteroids clump together and form their planets.
