Not sure what Walnut your seeing that is comparable to Hickory other than stuff that has a lot of sap. Walnut pricing is so high because there is a massive loss in yield because Walnut has such a thick sap layer combined with the fact that walnut tends to grow very bushy and often times doesnt make a lot of long/straight stems so your yeild per tree can be pretty low. Some people like the sap left in but for the majority of premium Walnut work people want only heart wood which turns an 18" diameter log into more like 14". When someone has a 16-18" diameter Walnut log and think they've got a gem, when its sawn without sap, they are shocked at how little material you get out of the log.
Some mills steam Walnut to bleed some of the color from the heart out into the sap and ignore the Walnut grading rules and grade it just like Red Oak but that means your left with miles of un-usable boards with tons of sap. You will often have 6"-8" wide boards with just a strip of heart wood up the center on one face and the entire other face and edges are sap. Additionally the steamed material is much more bland than un-steamed but the trade is its much cheaper even with the addition of the steaming process.
Hickory in my world is very white with dark accents but far more white than even sappy Walnut. Its brutal to work with, hard on tooling, very heavy, and due to the wild color has a pretty limited appeal (usually to people who like loud/wild/rustic grain/color). Demand for Hickory in my world is very low. Rustic log home kitchens, country folk, etc..