They failed because they over invested in near 0% interest US treasuries, and then the Fed rapidly hiked rates to 5%, quickly collapsing the value of those low interest treasuries on the market.
The investments themselves, and the promised return, were always "risk free", but the house of cards collapses when everyone demands their money now. And when people are looking at their savings interest rate of 0.1%, and seeing other banks offering 4%, it becomes very easy for a bank run to start as people simply move their money chasing yield.
The problem seems multi-faceted and complex, and like most complex problems, true blame is likely diffuse and shared amongst everyone, the customers, the banks, and the Fed. This is usually the kind of situation where societies elect a scapegoat to murder so they can all go about their business pretending to solved the problem and purged the evil from amongst their ranks.