The Member States of the European Union, after a messy compromise, managed to agree a banking union. This hotchpotch has been roundly criticised for its inability to achieve its primary goal: avoiding the collapse of banks.
Instead of creating the stated goal of pooling the rescue, the finance ministers have diluted the national responsibility for saving banks by forcing other stakeholders and depositors to pay too. Thus, uncertainty and fear for investors is increased by a complex system that regulates banks at a supranational level and forces national authorities to undertake the rescue. Is that not similar to having a unified central bank and leaving national authorities responsible for dealing with monetary decisions over which they have no control. That worked well!
This system faces a further hurdle. The European Parliament is unlikely to pass the union in its present form. They would wish to see rescues undertaken by the Commission reducing the role of the Member States. A statement of "provide the money and we will take care of the rest". The whole system may yet founder on this rock.
For why are the states unwilling to pool their rescues? Are they aware of the debt lurking within their banks? Perhaps they are unwilling to share the bad debt with the good. Remember, unless you are Greece or Cyprus, there is always someone worse off than yourself.