However we still don't see many people using it. Wondering if this is an execution/technology challenge or a use case no one wants...
Note that people use text based messaging even though audio messaging is available and provides an extra element of emotion.
I can see people going to the extra effort of making a video mail rather than a voice mail in circumstances where synchronous conversation isn't possible and meeting in person is out of the question. But I can't see what those circumstances might be, outside the sci-fi trope of "spaceship crew keep in touch with their families back on Earth". Keeping in touch with high-security prisoners?
I can see ambient video connections being useful --- when you have a screen covering a wall showing the view into someone else's room, and visa versa, so you can get an impression of how busy and what sort of mood faraway people are in without them having to explicitly tell you; and start conversations when you're not interrupting. But that's possibly more useful for business, and not video mail.