Well, now that you mention it. My take on this is pretty subjective because I am not a native english speaker. While I watch a lot of english-movies these days, I was brought up with a rich world of overdubbed movies in my native language. These overdubs tend to have a very good quality when it comes to clarity because they are always done in a studio afterwards.
When I started to watch english movies, I was thrown into an abyss of very hard to follow dialogue, but that was mostly because I was not used to hearing the actors speak on set during whatever they were actually doing.
However, that said, I do also feel it is getting harder with more action-loaded productions, which is basically everything in the past 10 years or so.
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
I find the music and background noise is so loud in modern movies that I struggle to hear some of the characters talk.
I thought I was just getting old but recently watched some older movies and found they were much easier to hear.