On: Why do all these 20-somethings have closed caption...

[bzzzt]

Maybe when downmixing it to stereo. If you play it on a real 5.1 system (not a soundbar or other "Dolby Atmos" gimmick with less speakers) your dialogues will come out of the dedicated center speaker which will make it easier to follow. (most home cinema receivers even have a 'boost dialogue' function if you want to know what's happening in the latest Nolan film...)

[brokenmachine → bzzzt]

I have a good calibrated 5.1 setup.

I still find the dialog way too quiet in most movies and 5.1 TV shows, even turning the center channel up +6dB.

I could turn it up even more but it's ridiculous that it should need more than that.