For me, my ability to stick to a diet was predicated on my ADHD being properly medicated. I never reached the "obese" category, mostly because ADHD seemingly doesn't prevent me from sticking to an exercise plan, but I was in the "overweight" for most of my 20s because I wasn't able to focus consistently enough to effectively count calories.
Many people can't stick to a diet or exercise plan because they haven't been treated for a related problem. For example, many people can't effectively exercise due to joint pain which could be alleviated by physical therapy which is frequently denied by health insurance.
Additionally, the "healthcare system" includes stuff like nutritional and exercise education, public gyms, etc., all of which are woefully underfunded in the US. Worse, the programs which do exist have been heavily influenced by lobbyists (lobbyist influence on the Food Pyramid, for example, is well-documented). The corporate right to lie in advertising also means that much education is undermined by straight up lies in ads.
Many people can't stick to a diet or exercise plan because they haven't been treated for a related problem. For example, many people can't effectively exercise due to joint pain which could be alleviated by physical therapy which is frequently denied by health insurance.
Additionally, the "healthcare system" includes stuff like nutritional and exercise education, public gyms, etc., all of which are woefully underfunded in the US. Worse, the programs which do exist have been heavily influenced by lobbyists (lobbyist influence on the Food Pyramid, for example, is well-documented). The corporate right to lie in advertising also means that much education is undermined by straight up lies in ads.