I was thinking, “Man, there are so many chord changes ... The song then modulates up a minor 3rd (one and one half steps) to the key of Eb and follows a similar progression in the new key ...

This is the first ... where as minor chords sound more melancholic or sad. Locate the 3rd of our C major triad (which should be the note E) and drop it by one semitone, to an Eb.