The core problem is that many movies have the audio mixed for a movie theatre with multiple separately controllable audio channels. You might see this marked as 5.1 ; DTS; etc. In a typical home environment, you only have stereo sound. This means that the multiple audio channels have to be mixed down to two unless there is a separate stereo audio mix channel provided - basically never except commentary tracks. The shitty way to do it is to just take the left and right front channels which are mainly meant for sound effects and not bother to mix in the center channel which covers the dialogue. It’s still hard even if you mix in some of the centre channel.

Short version: asshole movie makers mix only for movie theatres, not stereo.