Then how do you explain that not everyone is fat?
That's missing the point. Most of the non-fat people aren't thin because they've successfully rewired their caveman brains. Their thin for other reasons beyond their control. (Genetics, upbringing, etc.) When you look at fat people that TRY to be thin, it's nearly impossible. Studies have shown that less than 2% of fat people who lose weight ever keep it off for more than a year or so.
That's the main point. Fighting against caveman programming is very difficult, and few people can do it sustainable.
Most alphas are alphas because of genetic programming or other environmental reasons beyond their control.
Most thin people are thin because of genetic programming or other environment reasons beyond their control.
You can't "decide" to become alpha if you're not any more than you can "decide" to be thin if you're fat.
You can shift from less alpha to more alpha, but it takes a ton of consistent effort, just like a fat person becoming thin.
And no, I'm not saying thin people are the same as alpha. That is just a metaphorical comparison to illustrate how hard it is to fight against genetics and environmental factors, which are mostly out of our control.
I'm also not saying you should give up. Strive to be the small percentage who can slowly improve and keep the gains.