Just one example: Westpac in 2010 had 6.35 billion reasons why it should gouge its customers.
The rest of the banks - not just the big 4 - are no different.
They work for their shareholders, not for the people who put money in their accounts. After the account keeping fees, transaction fees, EFTPOS fees etc are taken out, the small amount of interest earnt (at what, 0.4%?) is lost.
Any bank - or any employee of any bank - trying to tell you that they're doing YOU a favour is lying to you.
They pay under 1% interest on a savings account. They charge over 7% on a mortgage. The balance lines the pockets of the CEO and the shareholders, who very much appreciate that the average person isn't smart enough to figure out that the banks are little more than incorporated thieves.