A large butt thin wall thickness rod blank can be lighter in weight for the power rating, but will be less durable, not to a fishing situation so much as a transport, knockabout, step on situation. Thicker walls are more durable to a certain extent till you get to the point where you get decreased stiffness for the weight added.
Everything is a compromise and you have to pick the chacteristics important to you and the customer, in this case the 89MT has a better chance of being beat about in the back of a truck or boat, having heavier weights swinging and bashing it's structure than a blank designed as a drift rod for steelhead would.