Why not? You are free to modify your vehicle in almost anyway you want as a consumer. Should someone putting some rain shields on their window require licensing and government testing for it because it might break off? Should generic brake pads or tierod ends require independent government testing or approval to be purchased and used?

Regulations don't exist to save people from their own stupid mistakes, they exist to prevent systemic abuses and dangers to the public in the pursuit of profit. And we already know from endless examples that corporations will knowingly let people die if their decision will increase profit margins. Not to mention the public doesn't have the ability to properly test or verify corporate designed and sold devices. Unless corporations provide all documentation related to the design and materials and code used, they should have special restrictions and regulations beyond what the average person does.