Geust DDT: … past decades saw more inventive ways of linking their harmonies together than we hear now. It's the difference between Carly Rae Jepsen's "Call Me Maybe" (2012), which contains four simple chords presented one after another almost as blocks, and Alex North's "Unchained Melody" (1955), which, though also relatively harmonically simple (it employs about six or seven chords, depending on the version), transitions smoothly from chord to chord due to more subtle orchestration

That's cherry-picking one way. I could cherry-pick the other way and say that something like "King of The Road" contains only C, F, G7 in very simple progressions whereas Oasis' "Wonderwall" uses C, D, Em, Em7, Dsus4, A7sus4,G, Cadd9, G5, G5/F#/E and Em7/B with much more complex structure.

In general, my memories of late 50s/early 60s pop are that, with a few notable exceptions, it used 3 or 4 chords in very simple progressions.