Why do some universities not provide marking schemes for mock exams? When I was a maths undergrad, I did some mock papers. However the lecturers did not provide the marking scheme for us to learn from model answers. The reason given at the time was a mumbled 'university policy'.

My question is, why would a university have a policy of not providing the marking scheme/model answers for a mock paper?
The materials provided to students should benefit their learning. It is not clear, how the marking scheme would help student to understand the actual material. Knowing the marking scheme can help a student to prepare to a particular exam without learning all the curriculum (e.g. by focusing on what is assessed). This is known as surface learning, and is often considered as bad practice.