The interviewee doesn’t know what the day to day job will look like, so they may wind up talking about entirely the wrong parts of their skills & experience. The interviewer has a much better idea what they need to learn about the candidate.

Perhaps this is less of a big deal for a generic position that’s the same at every company, but if you are matching someone to a very different role than they’ve held before, you may be interested in only certain pieces of their resume.