As we've seen this week, the scrutiny of depositors is far more powerful than that of shareholders.
Edit: I guess the point is that without the threat of depositor scrutiny, shareholders would have no reason to care about SVB's poor investment decisions, since they were only a problem in a bank run scenario caused by depositors. Failing that, the only risk to shareholders would be regulators, and regulators weren't doing anything about this problem, they were enabling it. I think you're right about that.