You're missing the entire point, and quite deliberately so, in order to fat bash really, aren't you.
A person who becomes obese, from any of those factors mentioned (laziness, lack of willpower, and greed) to such that it impacts health, is not a fully sound person. Therefore, there are psychological (which is health) factors, at play. It goes against the whole instinct of any being to survive and remain fit.
A person who won't get out of bed to deal with everyday life, may suffer laziness, and a lack of motivation. WHY, though? It's not just because they are 'lazy and unmotivated'. When those factors impact your life and your health to an unhealthy degree, it's fair to say there are psychological (and thus, health) factors at play, at the crux of the matter. Just not if you're fat, apparently.
Because we still have disgusting members of society who love to spread hate about people's weight challenges in the form of 'lazy, greedy'. Go on, go tell an obese person they're lazy and greedy and see the change you trigger.
After all, all a fat person needs to do, is stop being lazy and greedy. Its infuriatingly that simple. If only it was socially acceptable to tell them this we could rid the world of all the lazy, greedy fat people. Oh wait, we've been doing that for decades - hasn't worked out so well, has it? That's what body positivity should be about - not telling people they are, in other words, worthless because they are fat. A person who feels they're worthless, won't be motivated to change, in most cases.
Utilise a shred of human decency, and common sense, and move away from being frustrated at fat people for being fat, and you may just see things you haven't seen before.
No one, and I mean no one, destroys their health as a goal in life. Poor choices which lead to such weight gain, are absolutely indicative of there being deeper problems at play. Eroding their self esteem will, I daresay, be far more likely to make the person fatter, than thinner.
Overeating to such a degree of obesity or morbid obesity, is health related. If it's not physical, there is psychological factors at play. There are swathes of people with such disordered eating, which results in the obesity you see each day, whom are undiagnosed and receiving no help. And when they try to access that help - are genuinely told by medical professionals that they just 'need to eat less and move more' (speak to a few obese friends about their experience of the healthcare system). Sounds very simple doesn't it - I wonder why it's not working? Obviously it just MUST be because we have swathes of the population who would much prefer to just be obese.
The medical profession you reference is why a dear friends cancer went undiagnosed for so long, until symptoms really progressed. The utter exhaustion and body pain she was complaining about as a young woman (whom was NOWHERE near OP's friends size)- was immediately put down to her being fat, and she was waved out the door with undiagnosed cancer, and not one test being performed on her. She is not a rare case - speak to any fat person about their experience of medical care they received and you'll see it's a severe, common problem.
THIS is why attitudes like yours towards fat people needs to change. It's as downright dangerous as the other end of the spectrum that people are complaining about.
These attitudes are often pushed under the transparent guise of 'care', and it's such an overused excuse.