...that too many of the songs are stage-waits, adding nothing that the movie dialogue doesn't already establish and faster.
There's a big difference between a long song, say, from something like Carousel that goes "My Boy Bill will be tall and as tough as a tree.... What if she's a girl? ... I'll go out and make it or steal it or take it or die!" and
one that goes "With One Look...With One Look...With One Look...." or "Sunset Boulevard...Sunset Boulevard...Sunset Boulevard...".
Remember when Hammerstein advised Sondheim to take something that was good and make it better through music? And, by extension, discern when something can't be bettered that way.
Sunset Boulevard the movie is tight as a drum. The songs of the musical don't progress character or situation, with the possible exception of "Too Much In Love" sung by Joe and the girl near the end.