I grew up in the West and Midwest in the 1960s and 70s.
The first "jogging" boom hit in the mid-late 1960s. Doctors (e.g., Kenneth Cooper's Aerobics) started touting the benefits of aerobic exercise. So running hit the mainstream, maybe for the first time. Numbers were still kind of small; you didn't see many women out there, and men that ran tended to be middle aged, in cotton shorts an T's, often running at a track or early morning, etc. Kind of out of the way.
Coinciding with this, however, was the generation following on the heels Ryun, Lindgren, Pre. High school distance running became big in certain areas. And probably some of these blokes kept running after high school and college.
End of Vietnam war, Shorter and Wottle no doubt inspired post college runners to keep going. Rodgers' wins at Boston and NYC in 1976 were huge, and suddenly running became cool. Jim Fixx's book the Complete Runner was aq big hit and by the late 1970s it was fashionable.
(I recall Cram running sub 4 as a 17 yr old, back in 1978 or so--that made US news, so the era he's referrring to would probably be 1972-76, when he was just getting started and indeed it wasn't very mainstream yet at least in the 'states).
The second running boom lasted from the mid-70s to mid-late 1980s. Women's running became big time too.
As the boomers got a little older and settled into careers and such, things took a step back from the late 80s through most of the 90s. High school times fell off the charts and international performance by US and western countries fell off too.
Then came the penguin march. And as a popular "sport" it's been downhill since then. Indeed, the everybody's a winnner attitude (with the flip side of the coin that competitive runners are actually to be disdained) mushroomed. Then came the ultras and multi marathons a week mindset, where quality runinng means nothing it's how far, no matter how slow you go.
On the positive side, high school and college runners got back to basics and since the high school breakthroughs of the likes of Gabe Jennings, Webb, and Ritz the roll continutes.
So here we are. Post college/high school racing is on the outs, but mass participation/moving group hugs are in. Everybody gets a medal now and a few are getting very rich off the sport.