I don't think you really thought that sentence through, did you?
People are fat because they are lazy, active people are not fat. This is a proven fact. People don't cook good home meals because it takes a long time and its boring, and you're right - nobody even thinks to look up a youtube video or simple step by step online recipe because regardless if they can or can't make it, it'll taste like crap compared to sugary fatty salty calorie-ridden fast food they've grown accustomed to.. Even if they are eating unhealthy they can still work out 19 hours a day to burn off the extra calories, but are lazy and won't even work out for 19 minutes.
The only thing that is proven is people need to use more calories then they consume in-order to reduce weight. If the body doesn't have enough energy from food consumed, it starts to use its own stored energy (fat). That's why we say eating less calories makes you burn fat. You can still be lazy and loose weight simply by not consuming more calories then your body is consuming.
On the flipside, however, eating too many calories doesn't make people fat either.
Since a calorie is a unit of energy when food is used, you'd have to assume all foods are consumed and calories used by the body. This is simply not the case.
Proteins are not consumed by the body if they're not needed. Chicken for example, is already has a very low fat content. The calories consumed by your body from the chicken is considerably less if your body is already well stocked on it's protein supply. And while some vegetables have calories (since they do produce energy based what a calorie is) the body uses more calories to eat them then they give the body.
This is not simply about eating what you like and hitting the gym either (being active). There are plenty of people in the gym that are fat and will continue to stay fat for the longest time simply because of the foods they're sticking in their mouth.
If you're eating unhealthy foods and I'm not even talking about fast foods constantly here. The chances are your body is going to consume so many calories that its near impossible for the body to burn off the calories before the foods are broken down (mainly sugar) and stored as fat.
For example, if you're stuffing your face with pasta, potato salads and washing it down with soda all the time, and hit the gym straight way biggest thing you're going to be burning off (if you're lucky) is the sugar in the soda. After about an hour at the gym your body will be in a catabolic state. The sugars in the carbs will not be broken down and burned at the gym, instead it'll be stored as fat quicker. If you're eating that kind of foods you'd probably be better for you to go for a walk some hours after eating since carbs are more slow release energy.
I'm not saying people won't loose some weight being active in the gym, but unless they eat properly the gym is not much more help then walking the dog a couple of times a day.
A well balanced diet is far more beneficial then a active life style. Both combined is the best thing, but I stand by my original statement. I don't think people are becoming fat because they're lazy.