Until Rodgers and Hammerstein, and even after them most of the time, film musicals have very different structures than stage musicals.
Instead of spacing the musical numbers throughout the action, movie musicals tend to have a bunch of songs in the beginning and then few to none in the second half, as the plot is being wrapped up.
Also until R&H, studio heads thought the point of songs was to make hits to publicize the show and and secure the recording royalties, not to tell the story. So anything that hadn't been a hit on Broadway or wasn't a new attempt at a hit, was dropped. This, too, contributed to the relative scarcity of songs in non-R&H-type films.
Putting a film musical with five or six songs on stage only makes it seem slighter, so the tendency is to add a lot of "filler" to flesh out the evening.
I don't want to say it's never been done well, but no example comes to mind.
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Adapting non-musical films for the stage is something else entirely.