A request comes in: a form fill, a voicemail, a text to somebody's cell. Whoever handles the calendar reads it, works out what's actually being booked and how long it needs, checks availability, and replies with a couple of options. Then they wait. By the time the answer comes back, one of those slots is gone, so the loop starts over. That's a normal booking on a good day.
Reschedules are worse, because they cascade. Move one job and the travel between sites stops making sense. Move one interviewer and the whole panel has to re-coordinate. Meanwhile reminders are the first thing dropped on a busy day, and no-shows are how you find out they were dropped.
Add it up and the cost isn't really the coordinator's hours. It's the empty chair you already staffed, the crew idling between jobs, and the calendar that only works because one person holds the whole thing in their head.