There is not an auto manufacturer on this Earth that isn’t heavily subsidized by its government. The same industry, skills, and infrastructure that make it possible to build consumer vehicles also allow you to build military vehicles. In wartime, a government can come to an auto manufacturer and tell them, “you’re done making consumer pickups. You’re making army trucks now!” And domestic industry cannot be blockaded or embargoed.

And that’s not an industry you can just spin up overnight. If your country doesn’t have an auto industry, and you would like one? Even if you have an unlimited budget, it would still take you decades to get to the point of competitiveness. Countries have a lot of incentive to subsidize their domestic auto producers as a means of ensuring the country retains the ability to make its own military vehicles.