GTM ClubA call reaches the people who read email but never write back, and it produces a real answer in ninety seconds: interested, not now, wrong person. Nothing else in outbound gives that much information that fast.
It is also the channel most SDRs avoid, so teams that keep calling have an edge. The modern version is not a hundred dials a day; it is calls placed to people who already saw the email, with the trigger as the opener.