Why did military families receive exemptions from civilian labor services under the Ming system?

Under the Ming dynasty, military families were granted exemptions from civilian labor services as compensation for providing soldiers to the state in perpetuity.1

The Hongwu emperor established the weisuo ("guard-post") system to maintain the empire's military strength while minimizing the burden on the general population. Under this system, hereditary soldiers were often assigned state-owned agricultural lands to cultivate during peacetime, with the goal of making the military units self-supporting. Because these families were required to provide members for military service across generations, the state exempted them from the various labor services typically levied upon civilian households.231