Like I'm not saying it's inherently wrong, it's just, here are some negatives.
a. It focuses people more strongly on the final numbers, not the learning experience. And you get caught up in how important that final score is – sure, it's important, but not as a number; it's important because it pushes you to learn, to work like you never knew you could, to push through those walls, to better yourself.
b. It focuses on depth at the expense of breadth. You miss out on so much broader general knowledge from year 10 – you get to feeling that it's not important, because it won't change your score, but in reality, it's important for your life.
In the time that you spend 'fine-tuning', getting a 50 instead of a 45, you could have learnt way way way more on other topics. i.e. I think spending 3 years on one narrow subject is an inefficient way of getting the most out of your education, it leads to very deep knowledge of one small thing (where 'very deep' isn't even uni level anyway) and comparative ignorance of everything else.
c. May get bored/over it by year 12, so you won't have the motivation or enjoyment.
d. It takes your time away from social activites and building relationships with family/friends.
e. Expensive. Tutoring ain't cheap.
f. The fact is, you don't have an unlimited time to prepare in 'real life'. You'll only have 1 year to learn 1 year's stuff in, you don't have the choice to spend 3 years on it.
Imagine this.
Imagine a school decided that their sole focus was getting the best possible VCE marks. 'Let's choose a bunch of content-focused VCE subjects (ones with fewer 'skills'), like HHD, PE or Psych, and teach it all through school, from year 7 up to year 12! Then when they do these subjects in year 12, they'll all be getting 50s!
What's that you say? Kids need a bit of variety? Year 8-level cooking, sewing, woodwork, art, sport, geography, history, chemistry? What rubbish!!! They don't contribute to the ATAR, we are not having them!!!'
OK, they would probably get better VCE marks (assuming that everyone hadn't dropped out by year 10) – but they would have missed the whole point of schooling.