The word professional is the key here. In the dictionary it is defined as a person "engaged in a profession or engaging in as a profession or means of livelihood". Since profession is an occupation from where the professionals earn their livelihood, this expense has to be paid out of somewhere. Expecting the medical center to pay for the services of doctors, nurses and other staff would be a heaven at earth. Furthermore expecting the professionals to not get paid for their services would be implausible as they have to feed and live themselves. So therefore this cost has to come from somewhere, be it the patients, charities or the government.
Charities exist for the welfare for the people. They collect from the willing donors and distribute the income to take care of the needy. If a person is in need of an operation, a local hospital may conduct the operation free of cost for the patient, but pay for the surgeon and the resources used in the operation through the charities received. Interestingly, this process is not at all free since somebody in the society is paying for it. Even if that person is not the patient himself/herself, a member or members of the society are paying for the medical bills of that patient.
This sort of 'free' medical aid provision is also seen in some of the European countries and in the US.