Because food, materials, and money were being used for the war, so they had to even it out to spend it where they needed it most.
People in towns didn't have to give their produce to feudal lords and were independent if they paid their taxes, and the taxes were not as high as they were for people in the land. This caused many people to abandon their feudal lords and move to cities where they would work freely.
Answer:
to constantly improve our productivity, durability of structures and items, quality of products, ease, ect ect
