Example: sleep. Insomnia has a history which predates Shakespeare.
https://muse.jhu.edu/article/266971
In fact sleep patterns used to be different. It was normal to wake up for an hour or two in the middle of the night. But people went to sleep much earlier - typically around 7-8pm, woke up for an hour or two about four hours later, and went back to sleep again.
In spite of this insomnia was a known problem.
https://www.medievalists.net/2016/01/how-did-people-sleep-in...
So clearly going back to this pattern won't necessarily make everyone sleep better. And so "modernity" is not the issue, and the problem does not have a simple solution.
Likewise weight loss. Telling overweight people to eat less is like telling an alcoholic to drink less, or a depressed person to cheer up. It's pointless, silly, and naive and it won't work.
The real issue with weight loss is a combination of motivation and psychological reprogramming, with some addictive elements, plus education about nutrition. Also peer pressure. And access to healthy vs unhealthy foods.
There may also be underlying medical issues related to metabolism. (And - ironically - sleep patterns also make a difference.)
Again, it's not a simple problem.
This is not to say that tech non-solutions are better. But the idea that you can reduce issues that millions struggle with daily to a simple motivational sentence isn't any more realistic.
Or helpful.