While Williams alums come from every part of the world, it can be difficult finding alumni interviews in other countries - especially large ones. The admissions committee doesn't want to put people who aren't from the US at a disadvantage in the admissions process. Because of that disadvantage, some students who would have been admitted might not be. I think that the conversation went something like this: candidates should be able to effectively communicate their enthusiasm for learning and the College in writing, so interviews wouldn't significantly alter the perceptions of a large number of candidates. It does, however, constitute a barrier to admission for those who do not have alumni in their area who are able/willing to interview prospective students.