As anyone with a passing knowledge of US law knows, Louisiana is the only of the 50 states whose law traditions come out of the Napoleanic Code rather than the English common law. With the Louisiana Purchase including territory from what would eventually become over a dozen states, including it looks like seven in their entirety (Louisiana not, oddly, being one of them), why didn’t more state law codes develop out of the NC?
While the Louisiana Territory covered the future area of several states, only Louisiana itself had any significant population (with an existing legal system) at the time of the purchase.
Because the city of New Orleans and environs was the only part of that huge tract which had actually been settled by (French) Europeans before the purchase by the U.S. France claimed all that territory but it was inhabited only by Native Americans before the U.S took over.