Because doctors are humans, and humans make errors. I would never go into surgery without having at least a radiologist confirm the results of what the surgeon was seeing unless it was a life or death emergency.
Also, because people heal naturally at a variable rate. Not every tear or break needs invasive treatment.
Australian public hospitals have first class surgeons. In this case they recommended surgery. They're not doing it for financial gain, why not trust their advice?
Your alternative is to go to another surgeon for a second opinion but you can only do that in the private health system, and that will take months or maybe longer and cost you alot of money.