That's the problem. When they do it that way, they don't make a profit on BEV's. "Legacy auto" got good at building the supply chain network for parts. Then they pick and choose and assemble into a car. But everyone is taking a slice, and it's hard to optimize designs for efficiency between so many suppliers. Then they have their dealers to contend with.
What i'm saying is that "legacy auto" can certainly build and sell a BEV like they do with ICE. And it's not too hard for them to make that change, baring battery supply challenges. But they don't have the 30% gross margin that Tesla does. That margin will continue to grow and then turn into a weapon when Tesla needs to be competitive.