[BigZaphod]

I think it's mostly because it's hard to do other things while video chatting. Things like driving or walking or looking something up or typing, etc.

If I have a video chat window open, I feel sorta weird when I cover it up and go look something up or cover it with a notepad window to take notes, or a code editor to write some relevant code, etc. I feel like I'm rudely ignoring someone who's right there. And they have no cue this is happening, either, so they might assume it isn't and say something like, "so like this shows..." while briefly holding something up. And I can't see it just then because the window was covered. They had no way to know that I wasn't looking and missed it. Then there's awkwardness, repeating stuff, etc. It just feels slightly... wrong. IMO.

Edit: It'd be interesting if, while on a video chat, any windows or apps covering the remote participant "showed through" to them. I wonder if that alone would give enough sense of context to make it work a bit better?