How brokers get the benefit when they are providing free delivery trading?

As per financial experts, the broker's revenue mostly comes from intraday and derivative traders. Brokers do not generate huge income from delivery trading. Delivery based trading is very less, also to invest in delivery trading, the investor needs to pay 100% amount in cash. For brokers who are providing zero brokerage trading, the main source of income for them is interest on your money which is left unused in your account, as well as some brokers also do prop trading from the fund which is left out in their account.