Signature Bank is an example of the fears that the regulators are trying to contain. As depositors of Signature Bank heard that SVB was in trouble, they started yanking their deposits out on Friday in panic.
That's the potential risk. That even though it was a unique confluence of events that led to the fall of SVB, that anyone with deposits over $250k will question whether or not their money is safe. And that's why the regulators stepped in on Sunday evening.