Not all stars fly first class. I’ve know celebrities to fly coach. But your point is well taken, so let’s pose the question another way, what if the person in question was a longshoreman, farmer, construction worker, etc?
I'm a reasonably big guy at 6'2", 220, but I've never come close to spilling over an airline seat.). If a longshoreman, farmer, construction worker, etc. is so big that they require two seats, it's not because they're big and muscular. It's because they're morbidly obese.