I think one problem is that by the time the final mix is done the sound guys have heard the dialog so often that they know it by heart and don't actually need to hear it anymore, which is of no help to those who haven't heard it a dozen times before.
Thanks to big'ol_freeper for the center channel suggestion.
Try watching a British show from the 70s or 80s.
They’ve gotten better. (Faint praise)