<p>^^ exactly what I was going to say. These American universities are here primarily to serve America, although they have an international impact. Training foreign students, only to lose them to other countries, would be counterintuitive. Selfish? Perhaps.</p>
<p>In addition, it's not just medicine. It's generally very difficult to get into American schools if you're an international. But medicine is especially difficult, since many countries (especially Asian ones) bombard the US with med applicants.</p>