Beer, slow metabolism, and the fact that I've always been big.
At my lightest I was maybe 250 lbs with a 36" waist at 6ft2in tall. I eat less now, but I'm not as active both due to my schedule and my age.
I can't eat any less, and I don't have the time to ride as much these days. I sure don't have the time to exercise just to get exercise either.