How do we explain the utter failure of the weight loss industry, given that a huge amount of money, brainpower, energy has gone into scientific research; given that it is a major source of both psychological and physical suffering that decreases longevity and quality of life?
Money and profit are intertwined in all of this. The big food companies make most of their profits selling ultra-processed junk food to consumers. This junk food leads to obesity. Obese people support the "weight loss industry" you mention, and once again, there is huge money in this, whether you actually get people to lose weight or not (in fact, you could argue that there is more money to be made if people struggle for years to try and lose weight).
I'm not saying there are no weight loss programs that give good diet advice (there are), but there are also a whole lot of them whose diet/exercise programs are pretty much a complete failure (look at the TV show "The Biggest Loser").
Compared to the profits made from unprocessed foods, there is not a lot of money to be made selling processed foods for people (which would keep them healthy, if they ate more of it, and less processed food).
All the ultra-processed junk food consumption also leads to an epidemic of chronic disease (metabolic syndrome = diabetes, CVD, cancer, etc). This is great for the big drug companies, who make lots of $$ selling drugs like statins to unhealthy people. And this may sound harsh, but if you suffer (but stay alive) for years near the end of your life, the drug companies make more money off of you (as compared to someone who was relatively healthy up until the time of their death).
There is plenty of scientific research that supports avoiding processed foods if you want to remain healthy. So, the information is out there, and not that hard to find if you go looking for it. But you won't see the big food companies or big drug companies promoting the findings from this research (ever see a commercial on TV for vegetables?).
About 3/4 of the stuff for sale at the average grocery store is either processed or ultra-processed food (I prefer to call it "pseudo food"). Most shoppers have their carts loaded with this stuff. So, the cycle mentioned above goes on and on...........