Anyone using the bank signed a contract that defined how a failure affects them. There is absolutely a moral, philosophical, and biblical truth behind honoring that contract.

Galatians 3:15: "To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified."

Proverbs 17:18: "One who has no sense shakes hands in pledge and puts up security for a neighbor."

Outside of that fact, the reason that the system is designed this way is to protect normal people from Rich people destroying these banks. If it were the way you're proposing, only the Rich people taking on the most risk and debt would get paid out, and every normal person using the bank would lose everything. We know this, because that's exactly what happened before the FDIC, which is the entire reason it exists.