That isn't how economics works. You can't cite a government mandated outcome and declare that the intermediary processes are cheaper because the government ordered more production of something. An "economy of scale" is something that happens in some circumstances where it is possible to increase production without incurring non-linear pressure on prices. Not a law of production or economics.

Most of the things we are discussing here are places where good manufacturing principals can bring the prices down, but it is only worth putting that investment in if demand goes up by a lot. As such government mandated outcomes often to come to pass just because the mandate ensures there is enough future demand as to make the investment worth it.

Of course the car makers are strongly involved. Things where there is no potential to reduce price don't get mandated unless they are already cheap.