Because it isnt a car paint.
Read the forum, and what he says about it. He specifically mentions its use on industrial farm equipment, railings and other high ware areas.
It seems more feasable to use than something out of a spray gun if you want mho. Also remember its meant to be BRUSHED on, not sprayed. Think about the stuff you use on your house, and tell me that will fade in a year? I dont recall a tin of house paint having to cost 4 grand before it was classified as any good.
Like they say, its lateral thinking, and seems quite feasable...