Why is buddha só fat?

That's not the capital-B Buddha, that's a boddhisatva, a Chinese monk now known as the Laughing Buddha. He's a symbol of prosperity and contentment.

A fat buddha represents good luck and friendship.

A bad diet and lack of exercise. The same way most people get fat.

So what You got against Fat People smartass??

Some fat guy said, that God was fat and looked like him.

A combination of bad genes, fattening foods and no exercise.

He ate way too many egg rolls