Kelly Anderson replied, "That design allows the link to telescope a certain amount in order to allow some slack as the coupler swings. It also allows the brakeman to get some momentum going on the coupler lever before tension comes on the coupler pin."
Building on what Kelly said if enough chain or links were used to equal length of the stretched out telescoping links the chain would be long enough to hang down and foul the mating faces of the couplers or get caught between the horn block and the buffer plate.