In the US at least, auto manufacturers have actually been on-shoring manufacturing for years. It is just that it is mostly automated factories.

Chinese manufacturers have a cost advantage because:

1. Chinese labor is cheap.
2. China's large population and large institutions combined with their recent history as a labor intensive manufacturing hub means that they have some of the most dynamic manufacturing capabilities in the world. Essentially, they are incredibly rich in the soft skill of creating manufacturing processes.
3. The chinese government gambled on EVs early and it appears their gamble is paying off.