I think a lot of the change can be contributed to FX becoming cheaper, easier and better. It created a race to the bottom for the most visually spectacular movie. And when it’s cheaper, you can throw more in at the same budget. Then the next movie has to throw even more in to outdo their predecessor.
Though I’m not disagreeing that culturally we have been on a steep downwards decline with regards to our attention span.
Ok, though we were discussing scene length, as measured by the stopwatch, not specific content.