No, the video actually goes into that. Directors think it's "more real" to have mumbled dialogues. But they seem to misinterpret that as "more mumble = more good".
It's a combination of both. Studios typically will mix the end result for the highest-end sound setups, which most people don't actually have. If you're lucky enough to have a full surround with the ability to properly dial in equalizer and other settings, you probably won't have a problem hearing the dialogue even when it's mumbled. But on conventional tv speakers, it can easily get lost in the mix.
This video was exactly what first came to mind when I read "badly understandable dialogues"! It bothers me that as we got better mics, the actors became more unintelligible instead of the other way as one would predict.
I hear this all the time, and maybe I just don’t watch THAT many shows/movies, but I haven’t come across anything where the actors sound like they’re mumbling. Do you have a few examples I could look up?
I've used subtitles for most of my adult life, ever since having kids. First it was so I could watch without waking the baby, and then it was so I could follow along over all the noise in the house. And I never went back. So as sound mixing changed and got muddier, I guess I didn't notice, because I was already used to not being able to hear half the dialogue anyway.