On top of all this there's the theory that gas giants typically migrate towards their star, it may be rare for a gas giant like Jupiter to find a stable orbit where it can shield the habitable zone

Another thing making earth rare is its high proportion of iron ore. That and our abnormally large moon are thought to be the result of Earth colliding with another large rocky planet. The tidal force of an extra large moon + our extra ironey core give us an extra strong magnetic field to keep the nasties out and hold our atmosphere