They have complete vertical integration, China owns everything from mining operations to the refinement, to the production of the battery packs. Any non-Chinese manufacturers are going to have to pay ~2x as much for battery packs, especially in Europe because China won't sell them as cheap to our manufacturers as they do their own and we have environmental regulations preventing us from doing large scale lithium refinement AFAIK.

Not to mention that there's a subsidy that China pays on all NEVs, regardless of where they're sold.