So why not just provide students with officially sanctioned practice papers that are not past papers and also guaranteed to not share questions with the actual exam?
If you write a new exam paper every year that is also guaranteed not to share questions with the actual exam. From a professor’s point of view many questions that are superficially different are similar enough to practically be the same question. There are many, many questions that ask about what the real cause of the French Revolution was, or test to see if you will recognize that this problem is basically a red black tree.