why do you think the author showed German soldiers, such as Hans Hubermann, performing civillian tasks instead of being shown on a battlefield? and why did he focus on ordinary German civillians during wartime?

This novel isn't about battlefields; it's about the people. There was far more to the war than battles. The decision to write this novel from a civilian standpoint makes it more human. In it we experience the hopes, fears and suffering of the people who don't wear uniforms.