Because they are private banking records - some of the account info released is from private citizens doing nothing illegal (offshore banking is explicitly legal in many countries)
One way to look at it is: how would you like it if it was discovered that a drug lord was using the same bank as you to launder money, and therefore your bank account balances and recent transfers were released to the public, even though you had nothing to do with the drug lord other than storing your money at the same bank?