Rich chemistry is possible within only a narrow range of fairly low temperatures, and you find these in habitable zones that are close to stars but not too close. Our Earth’s orbit is in about the middle of our sun’s habitable zone. Venus and Mars orbit at the inner and outer edges, respectively, of our system’s habitable zone. But we are learning that some moons farther away from the sun, such as Saturn’s moon Enceladus, may also have internal furnaces and chemistries that make them life-friendly.
