From the Dead Celebrity thread the death of director Herschell Gordon Lewis piqued my interest because of this from the article about him:
Yes, while many of his exploitation contemporaries resorted to public domain or sound libraries to use and re-use music in their sexploitation or hyper-violent drive-in endeavors, Lewis’ background in music gave his filmography its own distinct flair.
This got my attention because both John Carpenter and Dario Argento are also musically inclined and, I believe, also composed music for some of their films.
Maybe that’s not enough to be considered a pattern but could there be something about horror film directors and music?