Because it has a lot of horse power. If you offered GT you are mega rich and you crux all around. You can't not to think that everything is cheap. Besides it needs to require some skill to afford a GT for a fast vehicle. It takes a lot of effort to created a GT.
This car is most probably a Veblen good, a good made artificially high to make it more desirable for the mega rich. Owning this car is like having a massive sign reading: "Hey look, I can afford to purchase a car for $400000, despite the fact it may be worth no-where near that much". The higher the price, the more certain the purchaser can be that they may successfully lord their wealth over others.
Of course, this may be the actual price realistically attributed to the value of the skills required to make this product. You can not put a price on workmanship.
Considering it's made in America, you could buy a Corvette Z06 3LZ (with Z07 and every other option applicable) or a Dodge Viper ACR for less than $130,000, and even European cars like the Ferrari 458 Speciale / 488 GTB, Lamborghini Hurácan and McLaren 570S cost less than $270,000. That being said, they are all much more powerful than the 592hp, 3.5-liter Ford GT. It also will be very fuel efficient at about 23 mpg on the highway.