Anen-o-me

There is a competing option of decentralized law where people make law for themselves and their property only using contracts, dispensing with even the arbitration agencies making law for people, and use arbitration only to resolve disputes that arise.

The Seasteading Institute is planning a seastead in the next few years.

Checkout /r/seasteading, I for one think you will be able to.

In Machinery of Freedom you explain how a system of dispute-resolution organizations (DROs) / arbitration orgs could offer packages of law for people to use, etc. (and it's a great book generally, thank you).

Why couldn't individual people to craft private law themselves or via their explicit agents via contract --why rely on orgs to make law that people then adopt?

If we're going to decentralize law production, why not decentralize it fully down the very individual? Then people who agree on basic legal principles can live together and create communities based around shared values in this way. Arbitration orgs need only become involved when there's a dispute.