Because it's an OLED TV. The KS9800 was great, but even the article you linked notes that the Display Quality is top of its class:
And that TV is $4,300 on Newegg. So yeah, not only are you adding the baseline, the Gsync Tax, and the NVIDIA Shield Android Box, and the subjective items like the niche factor, but then subtracting the subjective value of the objective fact that the same amount of money can buy you a much higher quality panel, then yeah, it's not nearly cut and dry on pricing as you're making it out to be. Not to mention there's absolutely no indicator that any of these panels are going to be anywhere near the quality of something like the KS9800, let alone an OLED Panel.
We'll know more when they're on the street, but the sharp curve of halo product pricing makes me thing you'll be paying for a $2,500 TV tops with the rest being NVIDIA gravy.