Even at places with quality flat carts for exactly this sort of cargo you gotta load and unload the carts. Also once you get more than 250 pounds on a cart that inertia gets fun. Nothing an able bodied person can't handle, but throw in an obligatory hard concrete floor and even humanly sized and fit people will require a period of adaptation to the task as they would any new exercise. A fupacabra though can barely adapt to moving their own body much less anything else.