You can't blame a lack of physical activity when the average BMR(sitting in bed all day) is 6500kj(1550~kcal) and the average recommend dietary intake is 7500kj(1800~ kcal). So bodyheat is claiming the vast majority of every human beings energy output, keeping us at 37c.
During exercise, a well known a side effect is heat generation, this increases the efficiency of that output. Cardiovascular exercise is lauded because doctors the world over read the number of deaths caused by heart disease, something which is cut by at least 50% with regular heart pumping activity.
So whats the main problem? The walls between 'entertainment' and 'food consumption' are being crumbled, thats all. If you're finding food to be your main activity, you're definitely gaining weight. Look at artists those fuckers are poles and its not just all the meth, they barely eat.