The rule is meant to keep CA residents from buying in places that have little or no sales tax. People were driving to Nevada to take delivery and then driving back into California 15 minutes later to avoid the sales tax.
This is a weird corner case that is not intended for your situation...
All of the major insurance companies are either pulling out of California or jacking rates sky high. The rate increases are across all policies and not just Rivian or even just autos. Home owners, renters, etc are all moving up dramatically.