Investment banks are securities companies in China. Securities companies can't absorb deposits, that is, they can't do what banks can do. If it is transformed into a bank holding company, it can not only retain the investment banking business but also absorb deposits. In this case, they can change the current predicament of insufficient funds for investment banks.
More importantly, banks can borrow money from the central bank, but securities companies can't. After Goldman Sachs and Morgan Stanley are transformed into bank holding companies, they can borrow money from the Federal Reserve, which can reduce the plight of insufficient funds.