I think there's probably one or more "real" filtering steps to start with, but after those steps there's still way more qualified candidates than positions to fill, and at that point the only possible solution is to choose randomly. But that's not "satisfying" so instead they just keep interviewing and finding reasons to reject people (all completely arbitrary, since everyone is already qualified) until they reach the target number, at which point all remaining candidates get offers. Which effectively results in wasting a bunch of everyone's time and then choosing randomly anyway.
(This is a massive oversimplification, of course, but you get the idea.)
(This is a massive oversimplification, of course, but you get the idea.)