Final answer:
The most likely motivation of the hacker group is financial gain through selling stolen credit card information on the dark web.
Step-by-step explanation:
The most likely motivation of the hacker group in the scenario you described is financial gain. By infiltrating the global financial institution's systems and stealing credit card information, the hackers can sell this valuable information on the dark web and make a substantial profit. This type of cybercrime, known as data breaches, has become increasingly common in recent years, with hackers targeting various organizations to obtain personal and financial information.