Intentionally giving a duress PIN which you know will wipe evidence - information you were just asked for by some law enforcement - just robs you of more of years and money. The law is lopsided and gives some more power than others. There's no point debating why it's like that, try to change the law before you break it or find ways to not need to break it at all.

The law here is destruction of evidence. The guy destroyed evidence by giving the wrong password to the police. If the police had destroyed it of their own accord, he'd be free. If the duress PIN was 1234 and the police just tried it, he'd be free.

There are all sorts of situations where people go free despite the wistful desires of prosecutors, due to the details of what happened and what the law actually says.

Of course it should be code. More specifically, it should be completely deterministic.

This idea that judges/courts can interpret the law however they feel like it in each individual case is what gives power to dictatorships. Then there is no way to know what is legal vs not, each scenario is different and the courts will inevitably choose what favors them. So yes, ideally, law should absolutely be "code" (deterministic).