Because, odd as it may sound, you don't go to law school to study law. You go to law school to train to be a lawyer. Those two things are not interchangeable.
When we say “study law,” we are referencing things like broad inquiries about the Constitution, examinations of the intersection of law and public policy, or ruminations on judging and judicial behavior. None of these topics are really part of the basic law school curriculum, because they don't really have anything to do with How To Be A Lawyer. So don't expect to cover them in a law school classroom.
What this means is that if you are the kind of person who likes to consider these kinds of interesting theoretical questions, law school will either bore you to tears or drive you nuts (or both).
Here's an illustration. Let's say you are taking your Torts final exam, and you are presented with the following hypothetical scenario:
A homeowner owns a swimming pool, around which they have built a fence to keep out trespassers (and they have hung a sign on the fence that says “NO TRESPASSING – PRIVATE PROPERTY” in big red letters) … one cold November day, while the pool's owner is at work, the towheaded eleven-year-old boy who lives down the block comes towards the pool … the boy has wandered out of his own house while his parents were home, but since his parents were busy smoking crack, they didn't notice him slipping out the back door … the boy sees the sign by the pool, reads it out loud (and is heard doing so by another neighbor), but then goes towards the diving board anyway … the boy then executes a lovely jackknife dive into the pool, which, since it is a cold November day, has been drained of water … the boy hits the bottom of the pool headfirst, breaks his neck, and is paralyzed.
You are then asked to determine what will happen … what lawsuits will be brought, and who will win?
Now, you make think that these potential lawsuits raise interesting questions, and you may want to explore them. Why should the pool's owner be liable, given that the child was trespassing and that his parents were getting high instead of watching him? Is this a good way for society to apportion risk? Would it be a good policy to force the boy's parents to have to foot the bill for his medical care? Is it a better policy to pass those costs on to the pool owner's insurers, since they would then compensate by raising their premiums so as to pass the costs on to the general public?
These are all intriguing questions. And at no point should you bring them up on a law school exam.
It is often surmised that the moment you raise a public policy question on a law school exam, the professor will think that you are trying to bullcrap your way through the test and will downgrade you. This may be an overly-harsh assessment, but it is not inaccurate.
Your job on the exam is to prove to the professor that you know about the doctrine of “Attractive Nuisance,” and that you know what will happen when it is applied in this case. Your job is not to offer a treatise detailing the flaws in the doctrine of Attractive Nuisance, identify how the doctrine marginalizes certain segments of society, and propose an alternative method of allocating risk. That's a broad policy question which is not at all germane to the exam. If you like broad policy questions, go to graduate school. Or try to get a job somewhere where such questions are tackled.