It may be a combination of factors. Bakers and Bookers are heavier, higher proofed and more expensive ($38-$52). Knob Creek, priced in low $20s, also features the most attractive packaging of the entire small batch line. Personally, I prefer the taste of Bakers -- but it's usually $40-42 in Miami.
You'd think JB would borrow a marketing page from Knob Creek and price the rest of the small batchers the same. But maybe doing so would cannibalize Knob Creek sales.