I often ask my American English native speaker friends this question:
When watching a movie in American English, do you turn the subtitles on?
Quite a lot of them say that they always do ("in order to make sure not to miss any details" is the most common justification).
My native language is Russian, and in Russia it is literally unheard of to turn the subtitles on for Russian movies. Everything that is being said is always 100% crystal clear.
Does this phenomenon arise because of how diverse American English can be in its pronunciation and vocabulary in comparison to Russian's?
Addendum: can this phenomenon be due to the fact that the connection between American English sounds and individual letters is much looser than it is for Russian sounds and individual letters?