The reason it's generally fairly high is because it's considered to be a specialisation of the medical/ health sciences. The course includes placements alongside the theory (this I know from a high school classmate) and is generally quite high in demand/ fairly competitive for few places, so it drives up the clearly-in ATAR. It's also a 4 year course, so that probably has a small factor in it too.
A look into the course can be found with the
course outline and
course Handbook and its appropriate units (subjects). Placements are generally in hospitals or medical imaging clinics (think: taking x-rays, MRIs, etc.); I recall my classmate saying something about rural placements.
It used to have an interview component from what I remember, but I just checked this and it seems to not have that aspect now. Now you just need the first aid, WWCC and police checks before placements.