To limit the probability of an inadequate footing width, which could lead to reduced friction among soil particles, which could lead to an inadequate bearing strength of the soil beneath the footings, which could lead to compressive failure and excessive settlement of the soil, which could lead to an inability to support vertical building loads or lateral earth loads.
This is to limit the probability of compromised structural integrity, which could lead to:
This is to limit the probability of harm to persons.