Apparently, Rick Berman found music on TNG and the later shows like DS9 and Voyager to be a "necessary evil". Ron Jones, who was praised for is work on "The Best of Both Worlds" said that the music in Star Trek after he was fired became "less melodic and more pad-like".

The first season is currently in the normal syndication cycle. So I never really thought about this until now. I do think that the music in the later seasons (I think that Dennis McCarthy was involved at this point) sounded a bit like borderline generic elevator/dentist office muzak.

http://www.startreksoundtracks.com/interview-ronjones.html