this will be because more recent movies will be utilising high dynamic ranges for audio, worked around by compressing/limiting but in doing so, you lose quality.
trade-offs for everything.
there was a time when stereo was seen as unnecessary faff, too.
edit: movies are mixed for theatres and no longer are the home releases adjusted to suit.
I'm guessing you're using a stereo setup then, dialogue is usually mixed into the centre channel, downmixing a 5.1 or 7.1 stream to stereo will produce those results.
even worse is if you don't downmix to stereo, and all you are hearing is front left and right, which is often just the reverb effect channels for dialogue
So a "desktop PC" isn't about its feature set or where you might put it, instead it is a form factor.