Sure, Napoleon replaced bad feudal laws with good ones. But the system maintains feudalism. Look at Mexico.
Common law grows, learns.
Polish law is based on codexes and it is not feudal - codexes meant exactly the death of feudalism. Also codex law "grows" and "learns" - there is a revision or a new codex made as a lucid and coherent whole every couple of decades if needed.
BTW, Americans DID import this French idea of the coherent logical legal structure. It is US Constitution.
Common law is a huge mass of improvised patches accumulated over countless generations. It grew beyond capacity of an intelligent person to grasp and even lawyers cannot understand it completely. That is why expensive lawyers can be so much better and that is why common law is perfect for the lawyers.