Well, law like religion or the economy or any human social system, invites the question, why should we have it?
Why should we have law? Law is ubiquitous. Even the most primitive societies have something like law or proto legal systems. Advanced societies have very developed, highly developed systems of law. Very different from one another, in many, many ways, but it's still recognizable as law.
So that immediately raises the philosophical question. What is law? And that raises a series of additional philosophical questions, it invites them. What is the relationship of law to other normative systems. To morality, a society's understanding of right and wrong. To religion, what's the relationship of law to other important dimensions of people's lives in any sort of society. The economic dimension of life, the political dimension of life.
There are ethical questions. What distinguishes good law from bad law? Just law from unjust law? Why should we make law this way, rather than that way? Should we be democratic in our way of making law or is there some better system than the democratic system? For most of human history, democracy was on the outs. Today everyone at least pays lip service to democracy, but are they right to, maybe there's a better system. That's a philosophical question about law making.
And then when it comes to the question of how laws should be interpreted, since laws are not self interpreting, human beings have to interpret them. Citizens in deciding what the law requires of them and understanding what the law requires of them. Officials, sheriffs, for example, policeman, mayors, governors, judges, handling disputes, which are often disputes about what the law is. Sometimes disputes about how the law, even if we agree on what it is, applies to a particular set of facts. Those all raise interpretive questions, which are in some measure, philosophical questions.
What does it mean to interpret a text? What does it mean to interpret a normative text? A text that's a body of norms, and laws are norms. Systems of law are bodies of norms, rules, and principles. So there's no avoiding philosophical questions about law. And those questions have been asked from the earliest days of philosophy.