I'll add one more reason -- TV shows often require you to pay attention to every word now.

Thirty years ago, if you missed a line of dialog, it wasn't usually a big deal.

Now if you're watching Westworld? If you misunderstand a single line that might be the entire difference between "solving" the episode or not.

TV has gone from a "casual" experience you can tune in and out of, to a kind of literary-precision experience that demands your undivided attention, for many shows. CC makes sure you understand every word, which just wasn't usually that important previously.