The short answer is that players in the "steel spikes" era pressured the ground through their feet to propel their swing much more than players do today. You can see the same move (to greater or lesser extents) in players from Hogan, Nelson, M. Norman, Knudson, Nicklaus all the way to a young Tiger Woods. You don't see that move much anymore because you can't create that much pressure in soft spikes. Also, the lighter equipment doesn't require as much ground force to be generated.
There are several excellent videos on Norman and this exact topic. Go to Youtube and search Greg Norman Footwork and you will find them.
Moderators...the videos were posted by another pro but not someone that Brian would consider a competitor (at least I don't think so). Remove them if you need to.