I'm assuming that what we are dealing with here is the speed of sound and if the lightning is too far away the sound (due to the distance and speed of sound) can't reach the point of the observer.
Thank you for the explanation!
In this case I guess what's new is that people are paying more attention to the sky. Which is also good.
It is still fascinating how lightning that covers such a large area of the sky and appears to be close, especially in the first video, still produces no sound. Guess it was really far away!