I think this phenomenon deserves its own thread, but something to bear in mind is that modern records are far longer than those released in the 1960s and 70s.
My Generation was 36 minutes long. Sgt. Pepper’s was 39 minutes long.
Nobody except punk and post-punk bands release records that short now. *Both *of Guns and Roses’ Use Your Illusion albums clocked in at over 75 minutes. The much more raw Appetite for Destruction was itself 53 minutes. The Black Album/Metallica is 62 minutes.
Maybe the easiest way to look at the phenomenon is to look at albums released by bands who recorded then and now. The Rolling Stones’ self-titled album was 33 minutes long. A Bigger Bang and Bridges to Babylon are both more than 60 minutes long. The Who’s Endless Wire is 52 minutes.