The thing that you are misunderstanding is that people don’t want to be humiliated about their weight. It isn’t that they want to be fat, but that they don’t want to be thought of as disgusting or “less than human” for being fat.
In fact, most people who struggle with their weight have worked harder to try to lose it than you can imagine. If you think “just eat less and move more” is something they’ve never heard before, you’re living in an alternate universe. It’s not always quite that simple; people have baggage, trauma, genetics, and so on.
It’s not that they’re proud of being fat. It’s that they’re proud of who they are despite their weight, not because of it.
The issue with doctors isn’t that they can’t tell patients they are obese and need to make dietary changes or lose weight; it’s that people will come in with unrelated issues and doctors will refuse to look past their weight to diagnose what the underlying issue might be, using weight as an easy answer to blame it on. Sometimes it’s weight; but sometimes it isn’t.