I always wondered that. It seems like it would cost the same to build a good looking car as a cheap car.
One thing, though, is practicality. It's harder to build a truly good looking car that is practical, i.e., can seat 5, has carrying capacity, etc. Look at all the cars in your pics, none of them have that. The ones with the best lines tend to be expensive "toys" where style comes first, practicality second.
Another thing is if the car is inexpensive, you tend to see them everywhere, so it naturally becomes less "exotic" looking, just by being so common. This may be an example of that:
But still, you'd think there'd be at least a few really good looking inexpensive cars.