As we know that banks are a business that promises big profits, banks collect money from consumers from savings to deposits, when banks get customers who want to save in the form of deposits, banks can freely rotate money, they give low interest to customers and apply interest high at least 2x so that banks get a lot of profit.
Thanks for letting me know your opinion, but I must tell you that I also resigned from a bank in 2014 for me to pursue a better goal, so I have experience also. What I iterated above are clearly not the obvious ways of generating money by banks, but I'm afraid that it is with it and its top employees and owners, these people are corrupt, only that they are cleverly doing it.
You might not know, but they do these and they do it cleverly to the extent that the CBN might not know, or connive with them for their own cut. Even if the auditors detected at times, they know how they settle their ways.
Try to investigate this online and you will be surprised by the bank frauds you would realize.
The big US banks such as Wells Fargo, JPMorgan Chase, Citi, have all at once point or another doing shady stuff or laundering money for others, before getting caught and being made to pay comparably small (for a bank) fines by the department of justice.
But I think banks mostly make their money off of interest rates, no? I mean, when you open a credit card, which is all too common nowadays, you are literally getting a monthly loan for the amount you spend and you have to pay that off at the end of the month, else the APR gets higher.