Anyway - I digress - it speaks for itself that we are debating the greatness of a band almost 60 years after their inception - I can't imagine people will argue over Robin Thicke, Ariane Grande and the rest of the current rubbish bunch.
I have to say thee chord/tone/ key change is interesting and unfair - there are many blues, jazz, and country and western riffs that resonate in songs over the decades.
I think that rather oddly I think that the launch of the digital era was the starting point - First of all I'm not sure about you, but Digital rarely has the kind of 'Moreish' sound that keeps you listening - it always seems on edge. We then have the convenience of track skipping - and then streaming and bit by bit we keep narrowing our attention span like a drug addict needing a quick fix hence the homogenisation of pop music.