Theme Music Abandonment

Theme tunes are a very important component to Films, TV shows and Videogames. Many iconic works are easily identifiable with their themes. Sometimes to change stuff up, a work's familiar theme music is missing from its latest franchise entry. This is often polarizing. Why it's done can usually be blamed on either creative or legal reasons. The appearance of this trope can make many people decry the work as Ruined FOREVER.

Compare with Theme Music Withholding.

Examples of Theme Music Abandonment include:

Anime

It's somewhat common for the final episode of an anime to not include the opening theme:

Cowboy Bebop
My-HiME and My Otome
Puella Magi Madoka Magica
So Ra No Wo To
The English dubs of Revenge of Diaboromon and the Digimon Tamers movies abandon their theme song in favour of the Digimon Frontier theme due to rights issues.

Film

The second film A Nightmare on Elm Street series is the only one not to feature Charles Bernstein's theme.
Batman Forever
Never Say Never Again, as a third-party remake of Thunderball, was forced by law to not include the James Bond theme, and thusly the original title track [1] could not be used for this reason.
RoboCop 2
Django Strikes Again never features Franco Migliacci's theme at any point, it would turn up as a cover in the Japanese remake/homage Sukiyaki Western Django.
Halloween III Season of the Witch: Was an attempt at a different storyline and is the only entry in the series not to use the theme.
The two Peter Cushing Doctor Who films.
All the X Men films have completely different themes, which is unusual for Superhero films.
The Superman reboot has some people nervous that this might happen.