Yes I know, I grew up running in the mid 70's and still run today. I also do some coaching on the side with middle school and HS runners.
In HS, 1,000 mile summers starting after freshman year, we competed in 13 or more XC races every season. Tripling was expected in track for team points. 1 week off after both XC and Track seasons and run everyday between. We did this because we knew everyone else was doing it. In college more of the same, but fewer XC races during the season as we were settling into the moribund 80's. As others have said, we raced significantly more than today's runners.
We ran in questionable footwear augmented with duct tape and Shoe Goo to make them last longer. We trained and raced on asphalt tracts. Rarely ran on soft surfaces (other than sneaking onto golf courses until we were shooed off).
Not sure why we did what we did but my guess is that we had fewer options than today's runners. We did not have access to computers, smart phones, treadmills, variety of footwear, nutrition based refueling options, asthma and thyroid medication, altitude tents, World Wide Web, portable music playlists, fanny packs, etc. I'm sure that if we did have access to all these things then we might have been different runners or consequently, the barriers to becoming a runner would have been lowered thus making running more accessible to the masses. As it was, running was fairly exclusive to those who could pull all that off without getting injured. I wasn't aware of any runners, competitive or not, who had asthma or other afflictions.
I also had no doubt that the good guys from the 60's were much tougher than we were so it made our efforts seem not so bad.
Disclaimer: I am in no way saying that what we did was better, smarter, or even faster than today's runners but there can be no doubt that we were tougher.