if you look at pictures from the 50s there seems to be very little seat post showing (2" or so) by the 60's the trend seems to have risen to around 6". Now it's about 3 foot..
If you look at old cine films of club rides from those days, they tended to ride fairly decent sized frames considering the average height of a man was a bit less back then. I think people just tended to grow a bit quicker than the bikes through the 60's and 70's, resulting in higher saddles for a given frame size.
Sanity generally prevailed though until the advent of modern-style road bikes with "compact geometry" and frankly weird looking frames in many cases. That combined with the idiotic fashion for stem slamming, which requires a short head tube, therefore an undersize frame, has made the appearance of many modern bike and rider combinations look like the rider has borrowed a kid's bike and taken that out for a ride rather than riding a bike built for a grown up!
My rule of thumb is spread your hand out and touch the crossbar in front of the nose of your saddle with the tip of your thumb. The top of the nose of your saddle should not be any higher than the tip of your little finger sticking upwards..