The pre-school education master has no requirements for undergraduate majors, and any undergraduate major can apply for it, so there are more people applying for it. Middle school education requires an undergraduate background. What is needed is to be able to teach two courses in Australian middle schools.
Recommended schools are:
Master of Education (Early Childhood Education)
Master of Teaching at Monash University (Early Years and Primary Education)
Master of Education (Infant), University of South Australia
Master of Teaching (Primary and Early Childhood Education), Deakin University