“Those stocks go into an account called cash which has a very small interest rate. “
stocks don’t “go” into an account called cash, one first SELLS stocks and then can sweep the funds into money market funds prior to re-investment elsewhere ...
and what you describe is not actually “cashing out” anyway, because all of those so-called money market funds are nothing more than short term bond funds, which is where almost everyone including the banks keep their short term funds, so “cashing out” of banks to try to “crash” them and putting the money in money-market funds pretty much just moves the money from bank pocket to a different bank pocket ...
your whole claim of withdrawing large funds from banks to try to crash them anyway is ridiculous; the people who put large amounts of funds in banks are the ones who own them anyway via capital ownership of the banks’ stock shares, so the last thing the big depositors/owners would ever want to do is crash their own banks ...
said, "the last thing the big depositors/owners would ever want to do is crash their own banks"
Once your stock is old it's not yours.