Well, disco had taken over in a big way by late 1974, so soul music - and by extension, a lot of soul-infused jazz - traded in its introspective, minor-key, black consciousness vibe for a shake-your-booty ethos. This is why I strongly prefer pre-1975 CTI.
There were other cultural changes circa 1975 also. In film, Jaws had created the paradigm for the summer blockbuster and the definition of a "successful" film. So a lot changed in Hollywood.
As a Morricone freak, I will add that 1975 is when Morricone split with Bruno Nicolai. As a result, his later scores lost some of the X factor that characterized his earlier work. (There are still some post-1975 Morricone scores that I love, including Exorcist II and The Thing.)
I could probably list more, but I'm on my first cup of coffee.