no, not all obese people chose or have a choice of being the way they are. especially in modern day United States. First of there are genetic factors which cannot be ignored. Even though this may account for a minority, it is still prevalent. Secondly, and probably the main reason, is the food available. While everyone says you can just choose a healthy diet it really isn't that easy. Healthy food is expensive in the US, and there is a huge portion of the country that just cannot afford it. Then looking at even the healthy food available, it's really not so healthy as you think.
I'm going to use milk as an example, and yes, I'm going to compare to Canada as it's the system I know. In the United States there are incredibly few restrictions on products such as milk about the levels of added hormones. this is because the US doesn't use a quota system for their dairy farmers, meaning they get very little for what they produce resulting in huge factory farms where the cows are pumped full of hormones and steroids to increase production. This results in incredibly poor quality milk with very very high levels of blood, puss (from mastitis, which is much more common), and hormones in the milk itself. Then when the drinker has this milk (along with all the other products with added growth hormones), they are most certainly intaking levels of them which are affecting their own body. Now the comparison to Canadian milk is that we have a quota system, where farmers get somewhere like 6-8 times as much for their milk. meaning small family farms can exists. there are also strict rules against the levels of blood and puss and hormones in our milk. It's actually why in Canada, we are not allowed to call milk from the United States "Milk". It has to be labelled as 'modified milk ingredients' or similar. but milk is only an example out of many. even the healthy food available just isn't that healthy sometimes.