All plants require different levels nutrients to grow. If the same plant is grown repeatedly in the same soil then the soil will run out of the nutrients that plant needs and growing that plant becomes difficult. By rotating through plants with different nutrient requirements, the soil can maintain a sustainable balance of nutrients.

We now use the scientific method to argue ideas, but in the past ideas could just be laughed at if people thought they sounded dumb. People laughed at ideas like the sun being the center of the solar system and doctors needing to wash their hands before surgery. Refusal to accept these ideas held humanity back from technological advancement.