There are key distinctions between cash and Bitcoin theft: Physically robbing large amounts of cash is really hard. Most people don't carry suitcases full of money, and bank robbers usually end up in jail or worse.
Electronic theft is difficult as well. If a bank believes a wire transaction was fraudulent, it can reverse it. And because bank accounts are generally not anonymous, fraud detection is a lot easier. By contrast, Bitcoin nodes can't undo a cryptographically valid transaction if evidence later shows it was fraudulent.
In addition, most bank deposits are insured up to a point by the government. Granted, you could privately insure Bitcoin deposits, but it's difficult to get the same scale of insurance that the Fed offers. Maybe at some point, but I'm not sure there's enough data points yet for an actuary to comfortable estimate the risks here. In addition, because insurance requires scale, the market for bitcoin insurance would probably consolidate into a small number of players very quickly, which raises the question of what happens if one of them collapses AIG-style.