In a major scale, I understand why the I IV V are the most popular chords mainly due to their diatonic functions and they also harmonize the entirety of the scale as they are the primary triads.
I was watching a clip of Ed Sheeran and he was saying "The whole industry... four chords!" and he was referring to the I - V - vi - IV progression.
Which got me thinking about the vi chord. I also recalled a study I read a while back where they did frequency analysis of chords and found that the top chords are I IV V vi. In C major (the key that all the songs were transposed to) the most popular chords were C F G am.
So I was wondering what it is about the vi chord that sets it apart from other minor chords in the major key such as the ii and iii? My current theory is that it's because the vi is the relative minor so maybe there's a tendency to want to go to that.
Please note that this question is solely about this vi chord and mainly in regards to pop music. I understand why the I IV and V are popular it's just the vi that I'm asking about.