The main reason markets existed historically was to ensure transactions were done in public. Prices were publicly observable, stolen goods were difficult so sel

The main reason markets existed historically was to ensure transactions were done in public. Prices were publicly observable, stolen goods were difficult so sell, etc. Having a single market everyone trades in does have efficiency advantages, but the main reason we have had organised markets in jurisdictions all over the world, for thousands of years, is because the people making the rules wanted transactions to be done out in the open to keep the people doing the transactions honest.