1. Credit rating decline: the bank will evaluate the credit status of customers. If the credit rating drops, the credit card limit may be reduced.

2. Poor credit status: If the cardholder fails to repay on time or exceeds the credit limit for a long time, the bank may reduce the credit card limit to reduce the risk.

3. Income change: If the cardholder's income changes, such as unemployment or income reduction, the bank may adjust the credit card limit accordingly.

4. Bank policy adjustment: Banks sometimes make adjustments according to market conditions, risk control requirements or internal policies, which may lead to the reduction of credit card quota.

To sum up, the main reasons for the reduction of China Merchants Bank's credit cards are the decline of credit rating, poor credit utilization, income changes, and bank policy adjustments. If the credit card limit is reduced, you can contact the bank to understand the specific reasons and take corresponding measures to improve the credit status, such as timely repayment and maintaining good credit habits.

Extended data:

Other related issues may include how to improve credit rating and how to use credit cards correctly. When dealing with similar problems, reasonable financial management and good credit record are essential to maintain a high credit limit.

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