Part of the problem with modern movies is they're designed for surround sound 5.1 systems or similar. In those systems, the middle front channel is generally used for dialogue, but that channel often gets entirely dropped when remixing for stereo systems. This predictably results in inaudible dialogue.
This was discussed on HN a few months ago, but I can't find a reference to that thread.
Some receivers have “dialogue boost” or otherwise let you adjust each channel individually.
More and more we just leave subtitles on, as too much dialog is easy to lose in the rest of the sound. I think it’s also a difference in how movies are made now; compare the pacing of Rocky with anything modern. Older movies stop the action to dialog; modern movies have quips over explosions
This was discussed on HN a few months ago, but I can't find a reference to that thread.