Because the Banks own the politicians who own the regulator purely because the regulators wages are payed by the government who treats our money and taxes as its own and does not act in the best interest of the tax payers or as the custodian of the economy.
Corruption in the Banks spreads to all areas of government. Tens of Billions of dollars of fines in the U.S. for Banks that have been washing money for Drug Cartels, funnelling money into ME banks known to support terrorism, market fixing, Financial advisor scams, property scams etc etc I wont bore you all with a long list.
CBA in Australia not to mention property scams.
Its enough to say that Banks own the Politicians who own the regulators, its that simple.