Many intros/endings aren't generic,
they are "emulations" of real things: take for example the movie&show track, it has intros/endings very similar to well known themes, Star Trek, Pirates of the Caribbean, Superman, and the problem it arises is the following:

1) You want to play Star Trek theme, and can't use that intro since it has wrong notes.
2) You want to play a different song, but you can't use that intro since if you play it, just after the first phrases people thinks "hey he's copyng Star Trek!"

So they are fairly useless...