An INDIVIDUAL payoff. Not the global one. By your argument, nothing stops the nuclear powers from destroying themselves. Yet somehow in the 60s the nuclear powers figured out the mutually assured destruction is also a prisoner’s dilemma and they COOPERATE despite the individual payoff being greater.
No, because if everyone else keeps their money in SVB and it avoids going under, there is no payoff for defecting - you simply disrupt your own operations for no reason by trying to switch banks.