Because Jupiter is so much further away than the inner planets.
The Earth is 149,600,000 km from the Sun.
Jupiter is 778,500,000 km from the sun
778,500,000/149,600,000 = Jupiter is ~5.20 times further away from the Sun than the Earth.
And with orbits they are not necessarily completely linear to distance because this depends on the velocity of the planets. If so then 1 jupiter year would be about 5.20 Earth Years, but this isn’t the case.
A year on Jupiter is ~12 years on Earth. I believe this owes to the fact that the larger the orbit, the slower the velocity of the planet. Mercury orbits 1.6 times faster than Earth, while Jupiter orbits at about 0.43 times Earth’s speed. And so Jupiter takes a longer time relative to Earth to complete its orbit.