I didn't become a physician, because my teenage-self unpacked being a physician as telling fat people to eat better food and start exercising -- for 50 years. Turns out there are other specialties... Despite thinking the human body is fascinating, I'm largely happy I don't have to tell unhealthy people to do what they probably already know they should do and then give them a bandaid for their gaping lifestyle problems.
They’re not even allowed to do that any more despite it being a legitimate medical risk (top 5 reasons for death according to the CDC are related to obesity).
Why not?
Patient reviews. So you can tell a patient they can lose weight, but if you do they might leave you a bad review. If you get enough of them, your practice might not keep you. Try few doctors own their own practice these days, so they have to care about patient satisfaction surveys.