I think you probably don’t exercise as much as you think then. 10 to 20lbs overweight is a lot.
Ever seen any football linemen, sumo wrestlers, or heavyweight boxers? Many of them watch their diet, but if you eat 8million calories of steak salad a day and only burn 7.5, there’s a chance you’ll pack on the weight. It has a lot to do with the genes.
I weighed 165 at my most athletic (way back in grad school) but I’m built like Fred Rogers and used to wrestle at 147. So I was carrying a good 15lbs in my love handles and belly. I routinely see folks walking around with over 100lbs of flab; 15 is really not much.