An important part of this is that there seem to be few real network effects in a video call per se. You don’t necessarily need an account to join a call, and you generally don’t need an application either, especially on the desktop - you just click on a link in your calendar and the call opens in the browser. Indeed, the calendar is often the aggregation layer - you don’t need to know what service the next call uses, just when it is…
Zoom has done a good job of asking why it was hard to get into a call, but hasn’t really asked why you’re in the call in the first place. Why, exactly, are you sending someone a video stream and watching another one? Why am I looking at a grid of little thumbnails of faces? Is that the purpose of this moment?