Because the aviation industry has powerful regulators and an absolute culture of safety first. Every mishap is dissected until a root cause is found, and steps are taken to ensure that root cause never happens again. After a major incident, it's almost impossible for the same incident to occur the same way again.

Nothing like this exists in the medical industry. In fact surgeons and doctors are notoriously anti-process, anti-statistics, and basically don't want anyone scrutinising how they work. I'm not sure how they've been able to get away with it for so long.