It's not really lazy, either.
Realistically, there is a limited amount of information they can test you on in the exam. You'll often find that exam questions are repeated, across multiple past papers and study guides.
They're not telling you the answer. You still have to come up with the marks yourself, memorise the content and get it out in a logical, sophisticated way in the exam.
There's a difference between telling you what's important to study and giving you an unfair advantage. It just saves you from wasting your time studying things which won't be tested (e.g. background knowledge which might be in the syllabus but it's not tested because it's just the context).