You realize these are separate divisions in a parent company and they just don't willy nilly use funds from the bank side to fund liquidity needs on the investment broker side right?
Not to mention they had their own hundreds of billions of dollars of "problems" to deal with.
and LOL we are coming out of a huge liquidity problem with banks thanks to COVID/mini crash of 2020. Almost all banks had to increase their capital reserves. a lot were forced to suspend dividends by the FED. Had to suspend stock buy backs, forced by FED. Forced to put additional 100s of billions in loan loss reserves.
Had to increase restrictions on loans, on trades, on margins, etc etc etc
They are 'expected' to be allowed to resume somewhat normal operations starting in 1Q 2021, but that is still subject to final approval based on the economy and covid.
Banks have 99 problems, they sure do not need a 100th and the sure do not want to get involved in something that will piss off the SEC/FEDS/et all.
That is why they still operate under separate divisions. Good old plausible deniability