This is the shittiest logic in the world lol. First of all, you assume that the ATAR directly shows how smart you are, which, it doesn't. There are thousands of people who get low ATARs and are far more capable in every way than people who hole themselves away in their room for 12 months to get a 99. Realistically, almost anyone is CAPABLE of getting an 80+, its more so a matter of interest and motivation, which not everyone has (especially as a teenage for gods sake, sometimes we barely have the motivation to wake up before 12). Not only this, A LOT of people decide what they want to do before they start high school. If this is teaching, then they already have a predetermined ATAR aim which is out of their control. If you needed a 70 are you going to turn yourself into a hermit for the sake of showing how good you are? Probably not, more likely you're going to spend a majority of your HSC life socialising and relaxing.
Also I think its worth noting, my one of my teachers received an asterisk on his UAI, he is far more capable as a teacher than any other of my teachers, including my Adv English teacher who is an ex HSC marker. There's a lot to be said about people who get low ATARs due to lack of trying - a lot of them are far better off socially, being far more down to earth compared to their 'high achieving' counterparts who are generally pretty socially stunted (but not always of course) and it just shows me you may be one of those people when you cite a correlation between teaching ability and ATAR. Also have a teacher with a masters in history, and she's fucking hopeless.