So? Those extra four years of education for people who want to be doctors are mostly waste, an elaborate hazing ritual. Make undergraduate entry to medical school a five or six year programme, like in Europe. The increase in physician career years will swamp any plausible decline in incoming student quality, even if they just admit students straight from high school to the current US med school system.

Selection bias.

That's kind of my point. How would an 18 year old know what they actually want to do without having spent some time studying it and other things? I went into school with intention of becoming a doctor and had changed my mind 2 years in. That's an expensive mistake if I hadn't been at a liberal arts school.