That is because back there society and lifestyle was a LOT slower. People had time to work and create with whatever gaming system that they had on hand, which in many cases were far more complex then they are now.
Most people today's society do not have the leisure time as they had back in the 70's - 80's.
Today it is the too fast paced, always on the go mentality.
Why you think board games have positive sales for 7 straight years. Casual Gaming is what it is now a form of entertainment.
And 5th ED is easy to use.