[ViridianFan]

You’ve also got to remember if they’re interviewing someone who is using an older device or one which isn’t particularly powerful not having the video means the computer can put more resources onto sending the video meaning you’ll get a better quality stream which is less likely to cut out. 

The other thing is that it’s not a traditional video call in a way. They’d have to patch through a feed from the studio cameras which wouldn’t  always have the presenter looking directly at the camera. Someone with more knowledge would know, but could patching the video feed from the studio cameras end up causing a delay?