Planets need the elements of Carbon Oxygen Iron Calcium etc. Time needed for stars to form. Formed inside massive stars.
Based on what weve observed in our own solar system large gaseous worlds like Jupiter seem far less likely to offer habitable conditions.
Another reason astronomers consider Mars. What would it be like to live on other planets and moons of the solar system. Formed inside massive stars. Other similarities to Earth come into sharper focus in the search for life.