Planets near the Sun are composed of mainly rock and iron. How does the Solar Nebula theory account for this?

The Solar Nebula Theory accounts for the creation of solar systems, stars, and planets. The theory accounts for planet composition by stating that iron compounds, silicates, and dust clump together to form planetesimals. Because of the proximity of the sun, ices and gases cannot condensate near them, so they do not become gas giants. The planetesimals then collide together due to gravity and collect to form our rocky planets.