I still don't understand what a "privacy card" is.
Can somebody which knowledge of this explain problems with "privacy" cards and why scammers love them?
Scammers don't care about privacy cards. They'll use anything they can get their hands on, metaphorical or otherwise. If it doesn't have their details attached, it's fair game to them.
Visa/Mastercard likely don't supply a way to link a physical card to it's virtual card generations (that'd be a security risk), so Google doesn't know that virtual card A is associated with physical card B.