It's easier to get people to agree to a process than a result, so processes make it a lot easier for people to work together.

The processes are imperfect and often take on a life of their own, but still tend to be respected, and are generally improved when the outcomes start getting too far from the spirit of fairness.

Transparent processes which involve specific laws are much easier to respect than opaque "wise elder chooses" processes. Especially when there are many wise elders who might have different opinions.