Some are still human underneath the fat, so they feel a need to have pride in their appearance, or even feel shame for being unable to control themselves. They put diet and exercise on a pedestal of impossibility, so makeup (which is actually harder and far more expensive) becomes something that they spend time on in order to "look good" despite their inability to face up to and address their real problems. Typically they either get to a point where they can't deny it any more and address the problem or they get to a point where they are so far gone they no longer can even care, and they either become human or give way to the obeast within.