Because they have fancy handles, and they actually paid a product designer to do some product designing.
Steel isn't the only thing that makes a good knife either, why would you pay hundreds of dollars for a Blue #2 Watanabe, when you can get a Tosagata for less money? Why would you buy a Tadatsuna made from GIN-3 when you can get a Hiromoto GIN-3 for less money? Why would you buy the new DT ITK knife even though its made from the same AEB-L as the Grand Cheff?
Steel is one of the easiest "technical" things to market, but the steel will no cut itself just due to its nature. If I make a hammer out of VG-10, its obviously going to be a lousy knife, so that presents the most important aspect of cutting performance, the form, or what is often referred to as cross sectional geometry. Companies will tell you that the knife is sharpened at a 15* angle, but that only tells you part of the story. Theres the whole area right behind the edge which impacts cutting performance. Obviously, it you take a 1" thick sheet of metal and put a 15* edge on it, the cross section is probably going to look more akin to an axe than a knife.
Theres also the heat treat, while you need a good steel to hold that 15* angle, it needs to be heat treated well, as well. A poor heat treat can lead to the knife being too soft, or too brittle, or have a plethora of various problems, and cutlery steel is nothing without a proper heat treat. There are even special heat treatments that bring out more potential from the steel rather than using the standard cheap and easy heat treatments. Even the best steel in the world is going to make a lousy knife if left in its annealed and unhardened state.