Financial institutions (banks) are responsible in handling financial issues, records, accounts and income of individuals, companies, churches and organizations. They respond promptly according to your demands on your accounts, they also have zero tolerance for fraud and are very security conscious, security intelligence and anti financial crime expertise but they've policies of not collecting dime from customers accounts yet banks are most wealthiest institutions on earth.
How do they make money?
* mortgage - using some billionaires account to buy housing properties and leasing them
* estate and lands with same patterns
* SMS alert charges
* Transfer charges
* Syphons dormant accounts or dead people accounts that are inactive with enough money in it.
* ATM and investment cards
* sales of currencies like dollar to naira
* preparation of international documents
* savings people's valuables like gold, certificate, court documents, WILLS, and so on.
This is what makes financial institutions very wealthy.
Most of the time, at least before the ridiculous inflation in the past couple years, banks were not particularly profitable and were mostly running on low margins, similar to supermarkets - where they made money from sheer volume of transactions instead of high profits from each one. Now though they are making lots more money between the amount they get in interest from the central bank and the tiny amounts they pay out to savers, while also able to easier hide profitable fees in growing mortgage rates.