The ROI for doctors comes over time. From uni to being fully qualified is a 12-15 year journey depending on the specialisation and how quickly someone chooses to pursue it.
You aren't earning money while at uni despite being on placement from your 3rd year onwards in a lot of cases. My brother is an anaesthetist it took him till about the age of 30 before he was fully qualified. Even then his work was largely in the public sector, once you build a reputation with various surgeons then you get on their private roster. That is when earnings accelerate exponentially and it's really just a question of how many days a week you want to work.
Tradies may earn more earlier but unless they setup their own company their pay ceiling is a lot lower.
