Why would we find more of the latter in planets such as Earth that formed near the Sun?

As the size, density, thickness, and velocity all coordinate with the distance from the sun, hence the rocky planets and gaseous planets differ from each other.

Explanation:

Our solar system consists of eight planets and one dwarf planet all are arranged in there the internal composition of elements the first four planets near the sun are made of rocks and have a core rest Jupiter, Saturn, Uranus, Neptune are made up of gaseous substances like Helium and Hydrogen just like the sun. Jupiter is the second densest planet in the solar system based entirely on gases and others like Neptune and Saturn made up of ice and magnetic core and terrestrial plants lack such due the violent solar winds blasted off this primitive atmosphere some 4.5 billion ago. Thus the gaseous bodies formed away from the galactic core that is the sun and have lower densities and planets like mercury have the highest densities due to their internal structure is used like earth and less distant to the sun and share some sort planetary atmosphere with that of the earth like venus.