Lack of competition dictates

Lack of competition is what allows Nvidia to price products however high it wants to and even lets its AIB partners go a little bit crazier with their custom cards. RTX is definitely a step forward in computer graphics but it will take time for RayTracing to become really necessary and get down to reasonably priced markets.

AMD cannot challenge this

It will be extremely hard and almost impossible for AMD to stay relevant in performance and high end gaming. With the introduction of Geforce Turing based 20 series RTX cards, Nvidia is putting in place a hard to reach distance between AMD Radeon graphics and Geforce. When we say Nvidia will rule high end in 2019, we of course mean the rest of 2018 too.