I think that your sentiment about fat people is true about 80-90% of the time around the world, but some places literally have food deserts which do not stock healthy options and in other situations even some folks might only be able to afford (financially or executive-functionally) unhealthier options that might either take less time to select or prepare, or cost less money or driving time to procure. I think that’s probably where the downvote is coming from is people who feel unable to escape obesity due to a variety of limiting factors in their day-to-day lives which inhibit them from taking preliminary steps. not to say that going on a walk or taking the extra effort is not within their control, but that some people still struggle with it anyways, sometimes for reasons that seem counterintuitive or like that they should not be a real issue to deal with in practice but wind up being so anyways for some people.