One of the fundamental problems confronting (historical) linguists is that of explaining why certain innovations arise and become full-fledged changes in natural languages, while other innovations die aborning. Not all innovations have the power of survival as part of the norm, and it is their raison d’être that needs to be addressed in any explanatory theory of language structure.
In that connection, following a line of reasoning that has been explored several times in earlier posts, one must keep prosody (“the metrical substrate”) in mind as a possible explanans––without, however, falling into the fallacy of the single cause.
A good candidate for such an explanation is the phraseological cliché “at the end of the day” that is constantly bleated about in contemporary media-speak (as elsewhere). Its prosodic structure is straightforwardly anapestic, i. e., with a metrical foot consisting of three syllables and stress on the ultima. This fact alone seems to have induced both its rise and its ultimate tenacity in contemporary speech.