That's because a lot of faculties tend to re-use their papers from previous years. Exam questions are hard to make unless if it's something like Maths or Physics.
I know a lot of faculties used to have lots of past papers but then they stopped releasing the past papers because they figured that they could re-use questions from there. ECON1101 and ACCT1501 used to have past papers but nowadays they don't get released for that reason.
As for MATHS, they are also on the library website; most 2nd and 3rd year MATH courses (excluding statistics) have past papers.