How does the government not know your income? I'd say that's more surprising (ignoring that neither institution would know about cash income or some deliberatel

How does the government not know your income? I'd say that's more surprising (ignoring that neither institution would know about cash income or some deliberately concealed income which it sounds isn't relevant). I've been getting regular spam from a credit card company to update my income as well. They probably just want another point of confirmation, or it's just a simple case of the left hand doesn't know what the right is doing.