its not THAT easy to get a 1 because you have to get 1s in most if not each element to get an overall one so if there is one part of an exam which pulls you down, it is harder to make up for that in a different part as the precentages are not added together, the score 1,2,3 etc is.
and the year i did standard grade maths (2 years ago) the mark for a 1 in each element was 84%