Why do many people advise people not to study medicine?

First of all, because there is a lot to learn, who can stand dozens of professional courses? The key is to remember the details and types of knowledge. So I advise you not to study medicine.

Secondly, doctors are very tired when they go to work, and they usually have to change shifts, which is very hard, so I advise you not to study medicine.

In short, it depends on your own interests and ideals. Just study medicine. Persuading people not to study medicine is mostly a joke made by medical students themselves.