For some people it isn't that easy, especially since there's so many fad diets and bullshit products out there that don't work for long if at all. They don't see progress and give up. Or it may be embarrassment or anxiety or depression that stops them going to the gym.

Eating disorders and other medical conditions are other possible reasons.

Some people just won't change their ways and expect the world to cater to them (pun intended).