Compared to other weight classes? Heard they have their weight in the back of their feet instead of the front?
They just have to move less. The much bigger you are, bigger will be the amount of energy needed to move.
I say the amount of weight makes the game a lot more difficult on the ground. 99 percent of men that big can't hop in and out & side to side extremely consistently, it's just not efficient. Escaping a corner and cutting off an exit seems to need more precision and deliberate movement than it might for a lightweight. Not to say there can't be athletic and nimble heavyweights, but the dynamic seems different. There's also the fact that you should step with every punch, and in that division, everybody can punch, so walking into shots and using your falling weight effectively are things to always keep in mind.