"It's normal and trivial for me; therefore, anyone who doesn't do it right must be lazy/greedy/insufficiently determined!"

There are so many ways that different people's bodies and brains are different, it is patently clear that the idea that it is realistically possible for every human to achieve and maintain what our current society says is an "ideal weight" over the course of years, no matter their physical, psychological, or financial situation is just another way for certain people to see themselves as more worthy and morally upright than others.