I know this is a huge generalisation, but I feel that there are more academically gifted students choosing the harder sciences and 4u maths than there are in the humanities. So perhaps that's another reason why so many of the higher ATARs come from the Science/Math combination. But when you think about it, with Law at USyd/UNSW at around 99.70, and students who do 4u maths, physics, chemistry etc. to the get the high ATAR, they might struggle with studying Law, which is a highly humanitarian based subject.