Why did only one part of the lunor module take off from the moon?

Only the ascent stage of the lunar module took off from the Moon because it was specifically designed to transport astronauts from the lunar surface back to the Command Module orbiting above. The descent stage, which contained the landing gear and other systems for landing, was left on the Moon to reduce weight for the ascent. This design allowed for a more efficient mission, as the ascent stage could focus solely on returning the crew to orbit.