I think the primary reason is that laws are about human convention, not real objects which one can clearly and deliberately define. Like at the most basic level nothing exists at all except for quantum fields or something like that. Everything else we talk about on a regular basis, people, dogs, streets, businesses, etc, is defined by convention to a greater or lesser degree.
It is therefore quite hard to create a formal system to refer to objects in the world in a way which induces no contradictions with intuition. This is why we have courts, among other functions of government.