<p>The cost of human resources, maybe? I imagine a lot of time and effort goes into converting international transcripts, scrapping together loans (because internationals can’t rely on Staffords or PLUS, and their own countries might not fund foreign study), sorting out US study permit issues, etc.</p>
<p>It might also be that professors are hesitant to take on students whose primary language is not English (silly as that may be in a lot of cases), or schools aren’t familiar with most international departments’ curricula and are wary that students might not have received the appropriate background (also silly, but we say it happens for small unheard-of colleges here).</p>