Why does Tally offer a return as opposed to interest on a fixed-rate safe?

Interest is a type of return specifically relating to a loan. When you deposit money with a bank, you are lending your money to that bank. The bank then loans or invests your money to make a profit. With Tally, your deposit stays put. Tally does not borrow your deposit from you to lend or invest for its own purposes, so interest isn’t applicable.