The bank manager can take more risks, knowing that the depositor's won't lose their money (over $250k if the bank they manage fails. Which is important because people tend to get mad when they lose large amounts of money.

Thus, buy bailing out depositors to an unlimited amount, bank managers are then incentivized to take more risks investing the depositor's money because the more risks they take, the more likely it is that one will pay out, raising the bank manager's bonus, and what their stocks are worth. Of course, by taking more risks, they also increase the chances that one will fail catastrophically, but since the depositors are all covered, up to an unlimited amount, eh.

If there is no risk, nothing is risky.