Why do people gain all their weight back so often?

Because we live in a society of constant, endless overabundance and most people eventually relent to the "norm". People like to eat, and when there is constant food around to enjoy, eventually most people will relent.

Losing weight and maintaining that weight loss is a never ending journey. And most people just aren't going to commit to that kind of never ending journey in the face of never ending food.

Doesn't matter how you lost the weight.
Doesn't matter if it was fast or slow.
Doesn't matter if you call it a "diet" or a "lifestyle change".

The overwhelming majority of people will eventually fall back into the overall cultural habit of overindulgence.

Because we live in a society of constant, endless overabundance and most people eventually relent to the "norm". People like to eat, and when there is constant food around to enjoy, eventually most people will relent.

Losing weight and maintaining that weight loss is a never ending journey. And most people just aren't going to commit to that kind of never ending journey in the face of never ending food.

Doesn't matter how you lost the weight.
Doesn't matter if it was fast or slow.
Doesn't matter if you call it a "diet" or a "lifestyle change".

The overwhelming majority of people will eventually fall back into the overall cultural habit of overindulgence.

That's a pretty bleak statement about humanity. I know a ton of people who've lost weight and kept it off.

It has nothing to do with "restrictions" in my opinion and rather has to do with a lack of focus on the long-term. People hit their goal and then rest on their laurels. They stop doing what they did to lose weight and instead fall back into their old habits. If you previously gained weight with those old habits, odds are you will gain weight again when you revert to your old ways. It's really as simple as that. It doesn't matter whether you ate pop tarts while losing weight or whether you ate whole foods while losing weight; it comes down to what you do at maintenance.

I think the *reason* people go back to their old habits is because they did restrictions that were temporary. Most people who learn how to eat PopTarts and still lose weight are the small percentage who actually learn something and are able to keep the weight off.

I'm sorry. I can't agree that the only people who 'learned something' and are going to maintain are those who learned to eat pop tarts and still lose. That's just a silly statement.

If you mean, the people who are most likely to maintain are those who learned to eat foods they like and still balance their calorie input and output, great. It takes a lot less energy to maintain when you don't feel like you're making big sacrifices all the time.

From what I've been able to see, there are a few different reasons that people gain the weight back fairly quickly. The biggest reason that comes to mind and the one I've seen a lot of, is that the person was following a restrictive diet without paying much attention to calories or macronutrients, they essentially ended up starving themselves until they lost the weight they wanted, then didn't have a clue as to how to proceed after that. Since they didn't learn much about portion sizes, eating certain foods in moderation, etc. on a self-imposed, heavily-restricted diet, they soon return to their old eating habits, which led to them needing to lose weight in the first place. Rinse and repeat, some people go through that cycle for years and years without getting anywhere.