People hate when I tell them the secret is proper diet and exercise, they just don't have the discipline.
Keyword: permanent.
Most people go on a "diet" to make up for (bad) habits. They make some progress. But then return to those original (bad) habits in denial that those were the cause.
Ice cream (for example) was poison then. Diet or not, it's still poison. A small bowl now and then? Sure. But a nightly night-cap? Nah. Healthy doesn't work that way. No one want to hear that, let alone change habits that limit such exposure*.
* My rule for the supermarket...if I don't buy it, I can't eat it. I'm convinced you would guess people's weight - and general health - by looking at their shopping cart.