I always find with ballads there’s a minimum tempo below which the song cannot hold together, like a certain amount of speed translated into centrifugal force is needed to keep a plate spinning I suppose.
(That bit may be cobblers ‘ sorry physicists.)
Anyway below this speed, which we shall call w (for Westlife), a song starts to drift apart. Particular details might be observable ‘ a pleasant string arrangement here, a memorable line there, but it fails to cohere, to capture the listening mind; or rather, to impose upon that mind its entire three or four minute structure. Sub-w balladry works best as drift music, giving the listener the sensation of being subsumed in the ebb and flow of a lover’s mind ‘ check the David Toop Sugar And Poison compilation for some good examples, or the longest song on any Al Green album. But in 1959 the conceptual and vocal technologies needed to achieve this had not been developed, and songs like ‘As I Love You’ devolve into a sort of ballad soup.