So what's the point of posting it? If it's so obvious and all that you really need to know, why are so many people still fat?

The unsaid part of "it's simple, it's just calories in calories out" is the implied "and people who don't get this are just lazy/dumb/it's a moral failing." Maybe this isn't what you are intending, but it is kinda at the root of a lot of hate that fat people get.

The discussion around weight is changing because we're starting to look into and understand the psychological components of weight, IN ADDITION TO the actual phsysiological processes of weight loss. Lots of "normal" day to day tips and "common sense" is being investigated and debunked. Shit is hard and complicated. Food is being engineered to be addictive. Some people literally don't have easy access to healthy food.