You seem to subscribe to the very mistaken idea that assemble means the same as make. It doesn't!
The major automakers build vehicles in the most efficient manner. Power trains may be built in one place, shipped to another for use in the total vehicle.
We built the railroads next Interstate highways and later airplanes to move people and goods around.
That is how they arrange for the components. People that design, engineer, plan, work in various places, too.
With very little publicity and fanfare, most major auto makers have design studios in California.
Management, financing, procurement, sales may take place in the home countries without which much of the profit potential and jobs opportunities would not exist.
Assembly brings together subcomponents from all over the great big, specialized world.
When we eat at a restaurant, we enjoy the benefits of services and assembly. The customers and restaurant employees and management create an end use for those Texas cattle.