I wonder who was running the PR for cardio and weightlifting in the 70-90's. For some reason weight lifting, and barbell training in particular, has a weird anti-intellectual connotation. Getting up to run for two hours at 4 am is the habit of a successful business executive, but spend a couple of hours a day in the gym and carry an excess of muscle mass and you're clearly dumb. It's very strange.
The Jim Fixx book "The Complete Book of Running" was a national best seller starting in 1977, then aerobics (studio exercise, a la Jane Fonda) hit, followed by Arthur Jones' Nautilus in 1986.
Free weights were considered "dangerous" for a long time. Frankly, most people who lifted back then were suspected of being homosexual.
If you take boomers as being born between 1946 and 1964, then the leading edge of the boomers were turning 30 about the time both Fixx's book and "Pumping Iron" hit the popular conscious. There is a lot more money in selling shoes to people than gym memberships, so saturation advertising is part of the 'why' as well.
I keep seeing this on HackerNews - everyone seems to convinced that keto, intermittent fasting, and fasting are the new holy grail, I am unconvinced. I am convinced in the good old "enough sleep and cardio" theory though, since both have known working mechanisms (incread blood flow and debris clean up during sleep).
why are you unconvinced about fasting? have you tried researching and reading the scientific articles about fasting and the other topics.
If you're thinking in terms of "holy grail," you may be subjecting yourself to an "all or nothing" fallacy.
Generally, we're discovering how to lead our bodies through the healthy operating conditions which kept our ancestors alive as we navigate a modern world of high-tech capabilities, treatments and availability crossed with widespread lack of discipline and healthy habits.
Go read some of Dr. Jason Fung's articles on his blog. Not saying fasting is a panacea, but doing it regularly unlocks lots of different health benefits. https://idmprogram.com/blog/
Sleep, and a mix of cardio and strength training would most closely replicate how our bodies evolved. Pre-civilization, humans would have needed both strength and endurance to make shelters and hunt. Both running, and lifting/moving heavy things would have been common.
Baby boomers are deadset on this idea that cardio is the only kind of exercise that one should be doing.