I think you may misunderstand how primary vs. secondary insurance works. If a credit card has primary insurance then that means that the policy provided by the credit card company will pay out before any other policies you may have including your own personal auto insurance.

If your card provides secondary insurance, then it means that your personal auto insurance (or other) policy would need to pay out first before the insurance provided by the credit card would kick in.

Now, if you don't have personal auto insurance coverage, then your credit card-provided insurance automatically becomes primary, regardless of whether your card provided primary or secondary coverage.

To put it another way, in the absence of other coverage, your credit card policy automatically becomes primary coverage regardless of whether the card provides primary or secondary coverage as part of the benefits.