For most obese people exercise is painful and its easier to sit on the couch eating than it would be to put down the heaping plate of chilly fries and go out side and walk for a bit. No people are lazy by nature. That is one of the reasons we have just a problem with weight in this country.
Its no really laziness, its about life style and most people are simply not willing to invest the time and effort, because it often is painful to do so, into changing things.
SO they sit at home, stuffing their faces, feeling bad about their weight, eat some more, get depressed, eat more, feel even worse, eat more, etc. The cycle is set and seldom broken.