My thinking was that it doesn't require a great deal of creativity to gather up a bunch of previous hit tunes and make include them in a film, even mediocre films are usually improved an average soundtrack. And the number of movies which include a handful or more of hit songs is almost beyond counting.
There is an interesting thing here. I agree with you completely that songs are often thrown in to bolster a bad movie, etc.
Sometimes though a single piece of music can be so masterfully paired with a scene as to change both the movie and the song in a very great way.
Scorsese comes to mind with numerous examples:
The Ronettes "Be My Baby" is so masterfully paired with the opening home video montage of "Mean Streets" as to forever change the song and enrich the movie in a way that seems impossible given how popular the song was. Also, Cream's raucous live take of "Steppin' Out" is used in the films final car chase/climax again to dazzling effect. In "Goodfellas", Donovan's "Atlantis" pairs with the violent demise of Billy Bats so remarkably that one can't exclude the two from one another moving forward.
Tarantino's use of "Stuck in the Middle" in "Reservoir Dogs" is a classic: a light hearted Jaunt paired with grotesque violence that forever imprints in your mind when you hear the song.
Kubrick' use of Vera Lynn's "We'll Meet Again" from "Dr. Strangelove" is yet another master stroke.
Also, in the realm of television, and slightly off topic, True Detective S2, as abysmal as the show was, contains a startling scene that is totally changed by the mood created by Bobby Blue Bland's "I Pity the Fool".
Many have taken advantage of this great technique and it is now ubiquitous, but the greats do it well and it is a technique that enriches the film, and the music, when done right.