Don't confuse prototyping with production. I've worked for GM and Ford most of my career and for the last 9 years before retirement with Lear Corporation. Lear is a Tier 1, 2, and 3 supplier. That is, we made wiring harnesses and multi-pin connectors we supplied to other manufacturers (Tier 3), we made subassemblies (Tier 2) and we made finished products that went to the assembly line (Tier 1). Our major competitor was Continental and we did cross work with them for the best interests of the OEM. Our customers were every automotive name plate from Hyundai to Rolls-Royce. We offered free engineering to secure the manufacturing of electronics. Profits were made by keeping manufacturing running 24/7. Because automotive assembly runs on the "just in time model" we operated manufacturing facilities in every major economy for control over JIT deliveries to the plants. We also operated global tech centers in the Philippines, China, Spain, German, Mexico, and of course the good old USA.
We even made automotive audio amplifiers that ended up with labels like Bose and other well-known names. Now Bose would fine-tune the amps to the vehicle but they made nothing.
We also owned copper mines so we could control wiring pricing. We owned injection modeling so we could make our own connectors, and we had ownerships in fabs in Spain to help manage the flow of semi-conductors.
I don't know who you work or worked for but I certainly have a much different experience than you. I've worked on both sides of automotive manufacturing, the supplier, and the OEM.