Silicon Valley Bank was aptly named: It held the funds of hundreds of U.S. tech companies and was a crucial player in the valley’s economy. But on Friday, it became the second largest bank failure in U.S. history after a rapid run on its deposits. Some $175 billion in customer accounts were taken over by the Federal Deposit Insurance Corporation (FDIC), which is now tasked with returning money to the bank’s customers. But more than 85% of the bank’s deposits were uninsured, according to estimates in a recent regulatory filing. That’s because FDIC deposit insurance is meant for everyday bank...