I’ve heard various explanations, I don’t know how accurate the following is. I’d be interested to learn more:

• the very earliest colony settlements had to bargain hard and with precision in order to survive. It began a contractual culture that eventually extended into litigation

• due to high immigration from many differing backgrounds, disputes had to be settled in litigation rather than relying on social understanding

• the religious culture was largely inherited from the Puritans who had a legalistic and inflexible reading of the new testament. (This unwillingness to compromise is why they were persecuted in Europe and fled to the new world)

• the American identity is ‘invented’ (in the sense that’s it’s an abrupt mixing of many old world cultures) and so national identity was initially based on cerebral activities (the Constitution, Bill of Rights) rather than evolved from a very long history of social bonds found in old world ‘nations’. This required a cerebral precision to be at the heart of identity which easily extended to legal rights and relations

As I say, take with a pinch of salt. But this is the gist of what I’ve heard from people who know more than me.