Did you ever wonder why banks are wiling to safeguard your hard-earned cash, often for free, or even at interest? After all, it costs the bank money to have tellers and branches and the infrastructure necessary to do this.
The main reason banks want your cash is that they want to lend it to other people. In other words, when you put your money in the bank, you are really lending the bank your money so that it can turn around and loan your money to someone else.
Banks quite literally play with other people’s (your) money.