Why does university want young people only to do medicine? School leavers?

If you are going to be a doctor your education will use up most of your youth because it takes a long time and a lot of effort. Universities want candidates that have a track record of energy, focus and high achievement so that they aren't giving a slot to someone that will likely drop out. Medical schools want successful alumni because successful alums tend to give a lot back to the school, as well as reflect honor onto their institution.

They don't