fat guys have plenty of muscle. I bet those sumo wrestlers have way more muscle than any bodybuilder.
a sumo wrestler isn't exactly your average fat guy.
They are professional sportsmen with a straight training regimen. You wouldn't survive one day with a sumo club. They get up at 5 in the morning, eat, then train from 7 to 12, rest, eat, then train until late evening, then eat again, sleep, repeat. Very hard lifestyle.
Not exactly what the average american does, sitting on the couch drinking coke and eating chips.