The extremely high penetration and usage rate of credit cards in the United States relies on the complete financial system and supporting credit system. In such a fully developed market, competition among banks is extremely full and fierce. Only by showing their sincerity (welfare) can they have a place in the market. A typical credit card will give you hundreds or even thousands of dollars when you sign up for the card. Even as a poor student, I receive invitations to open credit card accounts from different banks in my mailbox from time to time (not to mention the middle-class and wealthy groups with annual incomes of hundreds of thousands or even millions of dollars), which also reflects The intensity of competition. Under such competition, it is our cardholders who benefit.