I assume you are asking about the ones in the US system (because in the system like India and my country, everyone who finishes the med school are assigned rotational spots without exception). From what little I observed (almost all of the people I know get into residency in the 3-5 years of trying), some decide to become physician assistants, some medical scribes or some chose pharmacy school. After studying medicine for 4 years or more, one has sufficient knowledge about medicine to branch into similar professions like those.