I'm assuming this is referring to American doctors, because I'd say in most of the developed world, 'bonuses' like these are prohibited or significantly curtailed. In Australia, pharmaceutical incentives are limited to branded items (usually pens, post-it notes) of low monetary value and catering during an educational seminar, usually limited to $10 per head. But even in America, there are so many easier ways to make money than studying medicine. I'd suggest that a doctor's hesitancy to prescribe marijuana might be better explained by the limited body of literature to support its efficacy, especially as marijuana wouldn't have been in clinical guidelines during their time in medical school or residency, as well as the legal implications in different jurisdictions, social stigma and potential impairment in work, study, using a motor vehicle etc.
So yeah, "doctor loses a customer" is an insane take.