Earlier quoted context omitted.
Given that this is > $12,000 for a family of four, I'm guessing that it's not that much less, and at least half of it is carried over month to month, if not more.
Why do you assume that? I'm single but will sometimes have a debt of $10k in a month but never carry any over.
Mean (not median) household income in the US is $70k, I saw one source that it's more like 100-110 for married households with children.
It is literally impossible for those families to pay off a $12k balance every month. Factor in that you often can't pay rent, mortgage or car payments from a credit card and it's not even close.
(The fact that you save up and spend and then pay 10-12k in one month is irrelevant. Because of aggregation, what's relevant is your average month).