If it's like my aero books, quite a few manufacturers will in fact buy it. However, they need to make cars for everyone: you need to modify a car only for (largely) yourself.
You only need to modify to suit your personal preferences and local road conditions. They build for lowest common denominator-what they expect the broadest range of customers in the widest range of road quality and conditions to find acceptable. Which is why nearly every car rides far too high and too soft. It’s also why they almost all understeer, since it’s safer for bad drivers to under rather than oversteer.
