Hardly a mystery
Video conferencing has been around for decades, and these days it's as good as free, so it's fair to ask why we don't make more use of it.
Very well, consider it asked.
I do a fair bit of video conference-calling (several times a week, on average), and similar amounts of voice-only conference calling. I've used video calls for some years now.
Video conference calling is dreadful. I only use it when other people on the call want it. I find it offers very little advantage, even when there are no technical issues, even when most of the concerns people have voiced above (needing to look presentable, etc) don't apply, even when the attendees know each other well. At best people ignore the video; more often it makes them uncomfortable or serves as a distraction.
Many people (for example in comments on previous Reg stories about video calling) have praised video calls for some personal purposes, typically when calling distant family members. It's nice they like that application - but apparently many others aren't interested in it. (I'm not, and none of my family seem to be either.)
This is a technology that's been commercially available for half a century, and is now, as the article points out, nearly free for many users, but has yet to find a significant market.