My guess would be that the customers who are attracted to the Jim Beam name are not aware of or interested in small batch bourbons. Other factors may play a role in their purchasing JB, like price or nostalgia. The customers who are interested in small batch bourbons already know about JB's other offerings (KC,Bakers,Bookers).
Also, by introducing another label you run the risk of cannibalizing other products, like JB Black or KC.
The simpler the product offering, the less confusion, and the less potential for lost sales.