When Robert Justman left after season one, it left Rick Berman in charge of the music for the show. Justman liked lush, melodramatic scores while Berman preferred "sonic wallpaper," as it has been described. This led to Ron Jones being fired during the fourth season, and Dennis McCarthy and Jay Chattaway writing less thematic music as time went on.
What a shame that that happened. I didn't care a whole lot for the music in the later seasons.
I guess that's one more thing to blame Rick Berman for.