Another way of looking at it is that the patients who are refused treatment count as losses. So the current system is not actually maximizing wins, it's maximizing win percentage for doctors.
Ya, I went down this line of thinking too. It does seem like this might too be a poor incentive because now doctors would operate on everyone to try and claim wins, even if the likelihood is exceedingly low. There’s probably some measure like “healthy six months from now” that incentivizes them to try in situations with high mortality where operating is the only chance to improve things but keep them from operating if the risk is too high.