Larger clients normally pledge securities to trade, don’t leave free cash. Also, the yield on the float income is much lesser as the money gets used for a bunch of things (including quarterly settlement when funds are sent out). But yes, float income is revenue for all financial services firms (including folks who run wallets - paytm, mobikwik, etc). It usually contributes 15% of revenue for brokers. FYI last year Interactive brokers made a billion dollars in revenue just from the float income in the US.