First of all, it may be because the legal retrospective prescription has passed. According to the current laws of our country, the limitation of recovery of personal debts is generally five years, and it is impossible to recover through legal means after the limitation.

Secondly, considering the litigation cost and risk, banks may need to invest a lot of manpower and material resources to recover overdue debts and face certain litigation risks. If the amount of debt is small or the debtor's repayment ability is insufficient, the bank can choose not to sue to avoid the expansion of losses.

Finally, banks may also consider economic benefits. For long-term overdue debts, because the debtor has not made any repayment behavior during this period, it may mean that its financial situation is already very difficult, and the effect of pursuing overdue debts may not be ideal. At this time, the bank may choose not to sue, but try to recover part of the arrears through other means.

To sum up, the reasons why the credit card is overdue for six years may include: the legal retrospective prescription has expired, the litigation cost and risk, and economic benefits. Of course, in the actual situation, there may be other factors or conditions, and the specific situation needs to be determined according to the case.