Just guessing: One Type of Bottle where you can put on a different Label is way cheaper.
Not only the cost, but they are really trying to market this as a range of Single Barrel variations so all the same SB family
So far we have
Single Barrel Select
Single Barrel Ducks Unlimited
Single Barrel Barrel Proof
And soon will have ....
Single Barrel 100 Proof travellers exclusive
Single Barrel Rye
All with the same bottle, similar look etc, I personally think they are all too similar and the average consumer will make mistakes when grabbing one from the liquor store shelf but I'm quite sure Brown Forman know what they are doing.