Do you want a proper answer to that, or a cheeky answer to that?
Fuck it, I will give both.
Proper answer: The Hippocratic oath itself does not really make a statement about requiring pay, only that you will not cause harm to the patient. (and in the original version, wont do certain kinds of procedures, and wont instruct non-oath physicians. For clarity, when it was first introduced, the school of hippocrates was trying to distinguish itself from a fucking EPIDEMIC of faith healers, charlatans, and outright butchers literally fucking up patients worse off than they were before. A major source of this, was from botched up lens couching as a cataract fixing procedure. Improperly done, it blinds the patient, and requires very skilled and capable hands to do with the primitive tools of the age. It required an actual trained physician, but there were total charlatans fucking up eyes all over the place. To discourage the further proliferation of such horror, the school of hippocrates insisted that all students be PROPERLY trained, that all students swear the oaths to never do harm to a patient, and never undertake a procedure they were not competent at to assure this, and to never give medical training to those who had not sworn these oaths. It further, for moralistic soapboxing reasons, prohibited dispensing of abortive preparations to pregnant women, and a number of other things. For the most part though, it was to create a brand of integrity and trust in oath-swearing physicians, to fully hold them apart from the traveling charlatans going around fucking people up who were desperate.)
Cheeky assed answer: The medical industry as a fucking whole, abuses the good nature, and desire to do good, of every worker, of every level. If they could get you to work for free, they would demand you work for free.
While heavily biased toward US physicians and healthcare, it likely applies equally well to Eurozone physicians and staff as well.
https://www.thehappymd.com/blog/does-the-healthcare-industry-exploit-doctors