The reason is that one of the main investors of the troubled bank said that it will not be able to provide additional cash due to regulatory restrictions.  The bank in question is Saudi National Bank.

Saudi National Bank acquired a 9.9 per cent stake in Credit Suisse in 2022 in connection with a $4.2 billion capital increase by the Swiss lender to fund a major strategic reorganisation aimed at improving investment banking performance and addressing a number of risk and compliance shortcomings. Banks were already struggling under the US SVB debacle. This meltdown may be contagious to other companies and is a warning sign for the entire system. Following the fall in Credit Suisse's shares, there has been speculation that the bank might need state help in the future.

Performance of Credit Suisse Group during last 5 years. (Source: Investing)