I always enjoy science shows about space and our solar system. Many of them go into detail about how the solar system was formed and each time, it leaves me with the same question. The planets were formed by gas/dust/rock particles being attracted to each other and growing. Initially slow due to the small amount of gravity, but over the course of time, getting larger and larger and pulling more and more matter to form planets. Yet why isn't the asteroid belt in between mars and Jupiter, the Kuiper belt, or ort cloud not forming planets?