Why does the passage mention that the rover weighed only 26 kg?

Chandrayaan-3 was built to finish a job its predecessor had left undone. India's Chandrayaan-2 had reached the Moon's orbit, but its lander did not come down safely. The new mission had three plain objectives: to land safely and softly on the Moon, to drive a rover across the surface, and to carry out scientific experiments on the spot.

The spacecraft travelled in two parts. A propulsion module carried the lander, with the rover tucked inside it, from the rocket to a circular orbit about 100 km above the Moon. Then the two parts separated, and the lander made the descent on its own. Together they weighed about 3,900 kg, and the rover was only 26 kg of that.

Much of the engineering went into making the landing survivable. The lander carried laser and radio altimeters to measure its height, instruments to measure its speed, and a camera that could spot hazards such as boulders and steer away from them. Its legs were tested on a bed of material made to behave like the soil of the Moon.

The mission was planned to last one lunar day, which is about fourteen Earth days. In that short window, the rover studied which chemical elements lay in the soil around the landing site, and the lander measured the temperature of the ground and listened for tremors.