The problem is two-fold:
Firstly, our system is based on precedent - a law is only tested once. Trouble is, how different was the world or situation now from when it was first applied?
Secondly, if laws are generalised and open to interpretation, different defendants will be treated differently from each other even while committing the same crime. Sure, we know this bias already happens, but the bias is only introduced when there's wriggle-room. A rich man can afford an expensive lawyer, who in turn is rich because of their track record. It is possible to get a cheap but excellent lawyer ... but is it likely? And if a lawyer has an excellent track record then it's because of their skill and knowledge of law, the exeptions, the precedents etc. etc.
So ... laws are specifically worded, to reduce the ability for a defendant to interpret it to their own advantage. This, of course, makes actual explanations and definitions of laws complex.
Thirdly, while laws are constantly being examined as 'fit for purpose', amended or removed, the judicial system itself is incredibly hidebound and reluctant to change apart from superficially. There's the idea that "if a tradition doesn't affect the work you do, why change it?" There was a recent set-to where an organisation wanted to drop the prayer-blessing at the start of their annual dinner. Half were saying "Does it matter?" while the other half were saying "If it doesn't matter, why drop it?" You can imagine how thrilling that particular legal debate was!