I think part of the answer is what Cosmo is (perhaps inadvertently) doing.
Exercise has a key role in a healthy lifestyle and a healthy weight - it's impact on confidence, interest in health and metabolism being greater than it's calorific burn suggests.
But too often larger women (probably also men to an extent) are locked out of exercise because we had typically not seen images of larger women exercising. If you don't see it, you are less lilely to do it. If you do try it, shame or a fear of being judged by others may put you off again. Even the idea that you are not doing it properly because your body can not do the samer things as smeone thin. As a small example, if you have a large stomach then some yoga poses are not possible in their tradtional form - though there are great adjustments you can make for yourself. If you don't see or are not told of what adjustments you can make, you may see that your lunges or forward folds don't look like the instructors and lose heart.
You are also less likely to find good advice on how to start. Even simple things like knowing what kind of sports bra is more supportive if you have a very large chest or large back size. Or shoes that are extra cushioning for heavier frames. Or leggings that stop your thighs banging together. For sure this is all getting better but we still have a way to go.
Plus, and you se it all the time on here, the whole conversation around food and diet is still geared around the idea than you must suffer to lose weight. You must give up carbs, or eat 800-1200 kcals a day, give up treats totally, only eat foods you don't tend to like. I'm not knocking any of those methods but there are not enough conversations about how there is also the option to do it very slowly and gently and keep enough of what you like to eat to feel satisfied.
Finally, the diet conversations tend to be all or nothing. If you don't get down to a healthy BMI you have failed. This is crap. If you weight 18 stone and you get down to 16 stone, you still would have made a massive difference to your health. It should still be celebrated as a success and not enough people recongise that. Or that it is also a valid option to take a break, just focus on staying at your new lower weight for a few months before trying to lose a little bit more. The conversation is STILL focussed around messages like "lose a stone in 3 weeks" or "lose 100lbs in a year".
In short, conversations with many women suggest to me that thin or at, many have deeply unhealthy attitudes to food as a result of the disturbing messages we're fed around diet and body shape. It's so saddening to me.