During the hayday, we saw new companies come up with new cars all the time!!! And then they slowly went belly up. Part of me thinks that the endless number of regulations prohibited new car companies from entering.
You can import a car from china in a crate that fits on the back of a pickup. But it won’t be legal on roads until it gets things like a DOT approved windshield.
When was the last time a new car company was started, pre-EV?