If the EU requires all member banks to recapitalize all at once it could create a credit crunch. Everyone would be looking for money that didn’t exist. There would be no lending available for anyone else.
The same thing would happen if the EU orders all member banks to write down Greek bonds too much and take too much of a loss. That would make banks less solvent. If put through as a mandate all at once, lending would dry up.
In their zest to do something about the Greek credit crisis, they don’t want to do too much.