I always thought it would be cool if multiple habitable planets could exist as moons of some large gas giant and civilizations on these planets could fly around

I always thought it would be cool if multiple habitable planets could exist as moons of some large gas giant and civilizations on these planets could fly around the short distances of their planetary system visiting each other. Alas, it is not possible. Habitable planets can’t seem to really form as satellites for a larger world as explained to me once.