When you get into your 40s and 50s, food or booze often becomes one of your few rewards. You spend most of your time either at work, doing family things or chores around the house. So, chowing down on some bbq or drinking a few beers or eating some donuts for breakfast ends up being your treat for the day. When your metabolism slows, those treats easily translate into weight gain. At the same time, your ability to lose weight with exercise also declines in your 40s and especially 50s. So, you end up in a loop where you eat too much when you go out for a nice dinner, put on 2-3 lbs, can't burn it off and put on another 2-3 lbs because you were on the road for work and ate out a lot. An extra 10 lbs turns into 20 and then 30. Exercise gets more difficult as the weight piles on. Then, people just reach a point where they realize that they just can't drop the weight and give up on their body. And it helps that most of their friends are in the same boat (or look like a boat). 
I am about 25 lbs heavier than I was when I was training for marathons. If I eat out too much, I will put on 5-10 lbs and then really feel the weight. That usually gets me to snap back in line and drop some weight. But I also see saw back and forth between getting in some good running and lifting and sleeping in and eating and drinking too much. When you spend most of your day pushing a giant rock up a hill and come back the next day to find the rock at the bottom of the hill again, you are going to want beer and pizza for dinner instead of tofu and brown rice.