Here’s a brief video on how processing of sound in order to make it louder also makes it worse:
(The clip isn’t appearing in Preview, so here’s the direct link.)
The example is somewhat overdone, but there’s nothing wrong with that because it illustrates the effect. What you do know is that that dynamic compression (or remixing in some cases) to allow greater average levels can reduce the musicality of the music in a direction towards the extreme illustrated by this video.
It seems that the poster, who goes by the moniker LoudnessWar, is busily uploading a whole audio processing and production course onto YouTube. Check out his channel here.