The logic around that is:

If you're scrolling, it stays open. If you pause the video, it stays open.

If you stop moving your mouse, we wait a couple seconds then fade out. If you move your mouse, it resets the timeout.

Some people would scroll a little then stop moving the mouse to watch the current trailer and were expecting details to fade away since they were no longer interacting with it.

I think I understand your point, but it's tough when some people expect A and some people expect B.