We're talking Chancellor's Biomed, not the hundreds of students in "regular" Biomed. And of the regulars in Biomed, I would say if the Monash MBBS was available to them at the end of yr12, most would have snapped up the offer then and there. Many are there simply due to lack of a competitive UMAT score.
I am reasonably confident that the majority of those hundreds of UoM Biomed students know that they want to do Medicine
I'm not sure how you can be so sure though. I know people in Monash MBBS who weren't even sure they wanted to do medicine when they entered the course.
Another reason to take the Biomed pathway is if you really wanted to explore another area (eg. maths, chemistry, etc.) in some depth and then move onto medicine (MD) or dentistry (DDS). But the vast majority of those who aspire for med don't want to do this. If anything, that says something more than the few that take the guaranteed pathway. Just think, the median ATAR of metro Monash MBBS kids is 99.30-99.40, all of them chose Monash instead when they could have got into Biomed.