Why do the gas giants in the Solar System have comparatively large orbits compared to the inner planets? Ever since I observed the depictions of the Solar System, I was obsessed with the question of why the gas giants (outer planets) have very large orbits, compared to the planets that are closer to the Sun. Is it because of their mass or something I have ignored?
The current explanation for this is something called the frost line (which changes over time). At greater distances from the Sun, a body will receive less and less radiation, and so it will be colder than if it were closer to the Sun. Eventually, conditions become cold enough for volatiles to condense into grains. These volatiles make it possible for large-scale accretion to happen, and thus giant planets are formed. They may become gas giants (like Jupiter and Saturn) or ice giants (like Uranus and Neptune), depending on the composition of the protoplanetary disk at a given distance.

A graphic (from here) gives a better summary, although it's copyrighted.