The truth is, learning and habits begin and end at home. It doesn't matter what's taught in school if a kid goes home and their parents feed them junk and let them sit around indoors all day.
How can you claim with any validity that every kid in the whole country had the same education you did? That's ridiculous, you need to leave your bubble once in awhile. What about kids who are homeschooled? What about inner city kids who don't get education in these topics because their teachers are more concerned with getting them through standardized testing and preventing violence inside the classroom? What about kids who drop out of school? Nutrition education is not required for every American, it's just not possible to require educating literally everyone on any topic. So of course it's going to be missed by some (particularly in lower socioeconomic classes). Even in cases where nutrition education does exist, it's often barely touched on in PE or mentioned briefly in a one-quarter health class. Unless you were in a really good, well-funded school district--and not everyone has that luxury.
The only people who think weight is all about accountability and willpower have never struggled with weight in their entire lives. They may have been a little chunky sometime, but lost the weight without real hardship (I'm talking about you). It was easy for you, no question. But the amount of effort and willpower and hunger it takes some fat people to lose 10 pounds may be the same as the effort it takes a thin person to lose 30. Lots of people have decided it's not worth it. Not to mention, there are problems with ghrelin (the hungriness hormone) balance and satiety levels for fat people that someone who has never struggled with their weight has never experienced and can never understand (at least not without research, which you clearly haven't done).
You may find it easy to lose weight, because cutting down your food intake was relatively easy for you. Some people who try to cut down in their diet become rapaciously hungry 24 hours a day. And it never goes away. Would you deal with that for the rest of your life? Because statistics show that not many people can deal with it for more than a couple weeks. Most fat people that lose weight will gain it back within 5 years. All because their parents and teachers failed to instill proper nutritional and exercise habits when they were young.
So yeah, I think judging someone for having shitty stupid parents is a pretty dickish thing to do.