I do not understand considering that the training wasn't too different; all the amateurs races seemed to be much faster and your hobby jogger would also be much faster.
I noticed it first when Bryan Cranston talked about doing his first marathon; he just ran for 6 months-a year and did 3h15 for his first marathon in NYC.
Second, I checked the race results of a local marathon of 1993.
1500 runners
Winner in 2h15
First woman in 2h53
25 people under 2h30
150 people under 3h00
750 people (so half) under 3h34
Only 355 people above 4h00
6 people above 5h00
What were they eating back then?