The thing is, when you start having a lot of candidates at your door, say, because you are a big company with interesting problems and/or good benefits, and the

The thing is, when you start having a lot of candidates at your door, say, because you are a big company with interesting problems and/or good benefits, and the position is sought-after, your recruitment process costs even more. So you look to lower that cost by filtering out applicants based on some criterias. People from renowned schools go first because they are more likely to be skilled on average, if you ever deplete that pool, you look for the rest. I recruit for my company, and we don't do that, in fact we do quite the opposite. But I'm pretty sure that's how big companies see it.