“As far as the statistics are concerned, they surely have facts to back it all up.”
Actually, I doubt they have data to prove it.
In the absence of OEM levels of testing on every single aftermarket part, the safest position for the govt is to require the car’s to be kept stock, and that any non original parts match the originals in shape size and specification.
This is NOT the same thing as saying ALL aftermarket parts are unsafe. But without extensively testing the whole vehicle as a system, and testing to OEM levels (which is realistically impossible for a non-OEM), it is difficult to know for sure if an aftermarket part, which maybe very good quality in and of itself, will compromise the “system”
In Germany, the government tries to protect you by being really conservative.
Here in the USA, we tend to err on the side of personal responsibility. If you install a suspension that causes you to oversteer into an abutment, it’s your fault. But in truth, we all end up paying for that mistake via car and health insurance premiums. Same thing with smoking, scuba diving ... and racing cars. In the end the costs of these unhealthy choices are born by society.
I don’t claim to know what is better for society.