Think of a medical as a 'roadworthy'. On the day the vehicle was checked, the tyres were all within limits. You have so many days to get the vehicle registered, after which the assumption is that just maybe, the tyres are now worn.
As far as CASA knows, a medical standard achieved two years ago is no indication of your current fitness.
Everyone sees themselves as a special case, but the rules need to cover the lowest common denominator.