Well I'll shed some light on fat people as a fat person. I'm fat because my parents were fat and overfed me as a child, now food is a crutch like cigarettes or alcohol, you can become addicted to it, I've actually been losing fat recently by dieting, but it's very hard to do so, or else I would have done so sooner. People overeat to fulfill something in their life they don't have, love, acceptance, etc, whatever it is. Fat people know that if they eat less, they'd lose fat, but they don't have the willpower to do so, you need either a massive influx of inspiration (Like idk, you fancy someone and want to date them so you focus on yourself to lose fat because you think they don't like fat people) or you need to build up the ability to put the fork down. Remember fat people tend to be literally addicted to eating. (Feel sad? Eat, feel bored? Eat) and so on so this can be hard.

Obese people are more likely to be depressed on average than the average population, they're essentially slowly killing themselves.

Being overweight isn't genetic, but it's certainly behavioral. Put it this way, a normal person doesn't suddenly become fat for no reason, they tend to realise (Oh fuck what have I done putting on all this weight, I better stop)